Forensic DNA testing has been used to exonerate more than 300 innocent people, including 22 on death row. It’s helped capture dangerous repeat offenders and led to convictions in seemingly unsolvable cases. Yet, some warn it’s not the silver bullet it’s perceived to be. A recent study in Texas found DNA evidence was misanalyzed in cases dating back to 1999. Earlier this month, the Department of Justice announced policy changes to address concerns over the quality of crime labs that process forensic evidence, including DNA. Today, understanding the strengths and limitations of one of crime fighting’s most powerful tools.


  • Erin Murphy Professor, NYU School of Law; author of "Inside The Cell: The Dark Side Of Forensic DNA"
  • Daniele Podini Professor of forensic and molecular biology, department of forensic sciences, George Washington University
  • John Butler Fellow and special assistant to the director for forensic science, National Institute of Standards and Technology
  • Mitch Morrissey District attorney, Denver, Colorado


  • 11:06:53

    MS. DIANE REHMThanks for joining us. I'm Diane Rehm. DNA testing has long been seen as the gold standard of forensics. More scientific than fingerprinting, more reliable than eyewitness testimony. But recently, questions about the reliability of DNA evidence have begun to emerge. Here with me, John Butler of the National Institute For Standards and Technology and Daniele Podini, professor of forensic science at George Washington University.

  • 11:07:29

    MS. DIANE REHMJoining us from an NPR studio in New York, Erin Murphy, NYU law professor and author of the new book "Inside The Cell: The Dark Side Of Forensic DNA." I do invite you, as always, to be part of the program. Give us a call at 800-433-8850. Send your email to Follow us on Facebook or send us a tweet. And welcome to all of you.

  • 11:08:05

    MR. JOHN BUTLERThank you. It's good to be here.

  • 11:08:06

    MR. DANIELE PODINIThank you. Great to be here.

  • 11:08:07

    REHMGood to have you. Daniele Podini, give us a sense of how DNA evidence is used today versus how it was used, say, ten years ago.

  • 11:08:25

    PODINIThe methods that are in use today are significantly more sensitive so we are able to obtain DNA from lesser and lesser amounts of biological matter. So in that sense, it has -- the sensitivity has increased a lot. Also, the amount of samples that are submitted to laboratories has increased a lot so laboratories have seen DNA come from multiple types of crimes, not only homicides or sexual assaults, but also property crimes or robberies. So in that sense, there's a significant increase in the volume of DNA analysis as well.

  • 11:09:06

    REHMJohn Butler, how do you see how it's changed over the years?

  • 11:09:12

    BUTLERWell, as already pointed out, one of the challenges is that we have more sensitivity. When you have more sensitivity, it becomes a two-edged sword. You can get more data, but you also have to then do something with that data. The other challenge is DNA, in some ways, has become a victim of its own success because of the success in finding criminals and answering questions related to crime. The police now send in more and more swabs so they have almost a swab-a-thon where they're providing many, many swabs to labs, which provide lots and lots of data the lab has to then go through.

  • 11:09:45

    REHMBut hasn't that meant that scientists are called on to analyze a great deal more data than they used to?

  • 11:09:58

    BUTLERCorrect. There is a lot more data that they have to then go through and try to understand what's the meaning of that data.

  • 11:10:03

    REHMOkay. Here's an example. So say I have a pitcher of water and I pick up that pitcher and several other people pick up that pitcher and say someone who commits a crime picks up that pitcher. How are you going to discern which fingerprints on that are the fingerprints of the so-called perpetrator?

  • 11:10:42

    BUTLERScientifically, you can't tell the difference. All you can tell is you get a mixture of the multiple individuals that touched that and then you have to then try to figure out could that person possibly be in that mixture and that's what you're trying to figure out.

  • 11:10:54


  • 11:10:55

    PODINIYes. There's also another factor that is very important. The amount of DNA that an individual sheds varies significantly throughout the day and different individuals shed different amounts of DNA so you may have a person that touched it at a different time, but let more DNA than the last person that touched it. So that's a possibility, too.

  • 11:11:18

    REHMLeaving more DNA on one piece of...

  • 11:11:24

    BUTLERYeah, if you're sweaty, for example, you're going to leave more sample behind than if you're not sweating, so.

  • 11:11:29

    REHMErin Murphy, I know when you began your legal career, forensic DNA was just being introduced then and being used. How has it changed over the years?

  • 11:11:46

    MS. ERIN MURPHYYes. And so first, thank you for having us. You know, it's funny, the arch of my career, in many ways, was -- as a lawyer paralleled the real kind of rise and ascendancy of DNA in the system. I began my career right around the time that DNA databases really went online and the database was a true game-changer. The, you know, availability of DNA technology to confirm a suspect's identity was obviously, itself, important and did a lot to help bolster evidence in a case.

  • 11:12:16

    MS. ERIN MURPHYBut what really revolutionized the criminal justice system was the existence of these repositories of DNA where you could now, you know, take a sample from a crime scene where you had no leads or you had very little information and try to find those leads or find a suspect. So I started as a lawyer in 1999. The sort of databases grew over time, as did the technology.

  • 11:12:37

    MS. ERIN MURPHYYou know, when I began, the typing technology took weeks, months. You know, it was not unusual for prosecutors after eight months of waiting for results to call and the lab still hadn't been able to get to it. Now, we're seeing 90-minute typing machines. There are proposals to bring down the testing process even shorter periods of time. You see in high profile cases like the Boston bombing or cases of that nature, very rapid turnaround capabilities for testing because of these advances in technology.

  • 11:13:07

    MS. ERIN MURPHYSo it's really changed both on the database side and on the science side, the sensitivity of the methods and the rapidness of the methods.

  • 11:13:14

    REHMAnd now, let's welcome Mitch Morrissey. He's district attorney of Denver, Colorado. Mitch Morrissey, how big of a role does DNA evidence play in your prosecutions?

  • 11:13:32

    MR. MITCH MORRISSEYWell, good morning. It depends on the crime. Obviously, in a sexual assault, in a sexual assault homicide, DNA can play a very significant role. We're seeing it playing a much bigger role in property crimes like burglary. Not good in some other property crimes like auto theft, but just depends on the crime that you're looking at. I agree with everyone that's talked today. We've seen a huge increase in requests for DNA. I think, over the last two years, the increase to our lab has been 27 percent.

  • 11:14:07

    MR. MITCH MORRISSEYSo they get about 40 requests for DNA testing a week and so running about 2,000 DNA tests a year. But it gets a good payoff. The database, obviously, plays a significant role. We get about a 55 percent hit rate on DNA when it's put into the database and it goes from sometimes absolutely no suspect at all to potentially the perpetrator on the crime.

  • 11:14:34

    REHMSo how confident do you feel in results that get returned to you from the labs?

  • 11:14:44

    MORRISSEYWell, we just work with the Denver lab and it's a state-of-the-art lab, constantly evolving, evaluating the standards, their protocols. I'm very confident in the results that we get from the lab. I know that they are constantly training analysts. But that's the way the system works. It's just like anything else. You have to have strict standards. You have to follow your protocols, do validation studies, make sure the people that are doing the work are trained and can pass proficiency tests.

  • 11:15:19

    MORRISSEYAnd that's different throughout the United States. Denver is, I think, somewhat an exception sometimes to the rule.

  • 11:15:27

    REHMAll right. And Daniele, give us an example of perhaps using some other comparison of just how effective DNA evidence can be.

  • 11:15:47

    PODINIWell, you can imagine DNA as a molecular encyclopedia that cells consult when they -- during their lifespan and also when they develop throughout the organism. So a liver cell will look at the DNA part that -- the information in the encyclopedia to become a liver cell and so will a muscle cell or a neuron. And the entire encyclopedia, though, is present in each and every cell. So we can obtain DNA from any type of cell that contains this encyclopedia and for very low amounts.

  • 11:16:29

    PODINISo even from a touch sample -- so I can simply touch this cup and I can leave DNA. The fingerprints, instead, only originate from fingers so we can't obtain, you know, a fingerprint from a saliva stain, for example. So just a few cells can enable us to obtain the DNA profile of an individual.

  • 11:16:52

    REHMSo it's in, by comparison, say let's look through a looking glass, a magnifying glass.

  • 11:17:05

    PODINIYeah. So for example, if we were to look at this surface, the surface of this table with the naked eye, we'd see a smooth, clean table. Whereas if we look at it with a magnifying glass, we'll start seeing some ridges and maybe some fingerprints. Then, we zoom in with a biological microscope and we start seeing some bacteria and some other -- and dust. And then, we zoom in even more with an electron microscope and then we see all the ridges of the table.

  • 11:17:36

    PODINISo DNA is like the most sensitive of these. It enables us to see very, very minute amounts of sample.

  • 11:17:46

    REHMDaniele Podini, he's professor of forensic and molecular biology at George Washington University. Short break here. We'll be right back.

  • 11:20:04

    REHMAnd welcome back. We're talking about advances in DNA evidence. Here in the studio with me, John Butler, he's at the National Institute of Standards and Technology, Daniele Podini, professor of forensic and molecular biology at George Washington University. One the line with us from NPR in New York, Erin Murphy, professor at NYU School of Law and author of the book "Inside The Cell: The Dark Side Of Forensic DNA," and also on the line with us, Mitch Morrissey, he's district attorney of Denver, Colorado.

  • 11:20:54

    REHMErin Murphy, tell us where things stand right now. I wonder if the sensitivity and the complexity of DNA evidence can raise concerns for you.

  • 11:21:11

    MURPHYI think it absolutely can, and I think we're seeing the scientific community begin to embrace those -- that understanding as a result of leadership within the community that recognizes that as much as we love DNA to be the perfect technology that solves all of our criminal justice problems, it can't be that. It has to be taken for its strengths and its weaknesses. And I -- you know, in many ways I wrote the book so that we could have a conversation nationally within the criminal justice field about how best to use DNA, what are its limits.

  • 11:21:43

    MURPHYSo I would sort of highlight three different areas that I think are needing to be considered. One is just the science itself. When do we push the science too far? What are the open questions that we have about this technology when, you know, a DNA transfer in situations we might not expect it and so forth. The second are the statistics. This is a critical component of DNA. Unlike something like a witness description, where you just rely on your general knowledge of, you know, certain characteristics in the population, how common is a face tattoo for instance, DNA is opaque to laypeople.

  • 11:22:12

    MURPHYIf you say DNA matches, you have ask, well, what does that mean? Is this a significant match, or does it not matter? Everybody would match if you looked at just same plays. And so the statistic and understanding the statistics, how we compute them, how we tell them jurors. And then the last is social policy. Even when DNA works and works great and works well, I think that we do need to have a conversation about who do we want in our DNA databases. Who must be compelled to give DNA to the state? What kind of searches do we want done? What kind of testing do we think is appropriate? What traits are we allowed to look for or not look for in a DNA sample?

  • 11:22:48

    MURPHYWe have a kind of spotty history or checkered history globally, really, when it comes to genetics and criminal justice questions, and we're dealing with some very volatile information when we look at the whole genome. So asking careful questions about what testing should and shouldn't be done and what collection should and shouldn't be done.

  • 11:23:03

    REHMMitch Morrissey, how do you address first the science, the question of how far do you go with this science?

  • 11:23:15

    MORRISSEYWell, it's just like anything else. I mean, you drive your car too fast for the conditions or whatever, you're going to have a problem. I mean this science has limitations, it always has. Some of those limitations have been addressed. it's a constantly evolving field. So yes, I mean, we can push it to its limits, and that's usually where you get into problems.

  • 11:23:36

    MORRISSEYBut again, I think you're talking about standards and protocols and those types of things that need to be addressed. They need to evolve. I know currently one of the big things is the statistical analysis on complex mixtures. That's evolving. Our lab recently went through almost a one-year period of time where they were validating the use of a new statistical analysis system, and obviously legislators play a role in this when it comes to who goes into different state databases, what traits you look for, those kinds of things.

  • 11:24:12

    MORRISSEYYou know, right now the state labs primarily across the United States are looking at the same basic locations on the DNA. I think that it's important to remember that it's legislators that decide what traits to look for and provide the money for those kinds of testing.

  • 11:24:32


  • 11:24:33

    MORRISSEYSo the idea that you can look at the entire genome in a database or a crime lab is just not the case when it comes to DNA basing currently in the United States, and in order to do that, it would cost millions of dollars to the states to convert their systems to be able to look for the different traits and things that they're not looking for now.

  • 11:24:58

    REHMAll right, I think Erin Murphy wants to jump in.

  • 11:25:01

    MURPHYYeah, I think there's a lot of assumptions about what the law does and does not allow in this situation. So for instance, you know, an area of interest is this forensic phenotyping, the idea that you would look at a genetic sample for physical traits, maybe like a mug shot of the person, essentially, to come up with a picture of them. So that's looking at what could be deemed somewhat sensitive information. I don't think it's as sensitive as a medical or, you know, other types of behavioral propensities, but it certainly is more than just this kind of useless numbers type of genetic information.

  • 11:25:28

    MURPHYAnd when it comes to crime scene samples, universally in the law, it's agreed, a crime scene sample is what's called abandoned. It's kind of been forfeited by the criminal, which means there's no real legal regulation of what can be done to that crime scene sample, which is why we have seen in the United States crime labs testing crime scene sample for phonetic traits. There's, you know, a North Carolina case recently or an investigation recently where they put up a wanted poster using a genetic mug shot, essentially.

  • 11:25:58

    MURPHYAnd so that's a good example where there aren't the laws, I think, on the books people might assume, and that conversation hasn't happened. And I'll just tack on one little piece there. The same thing's true for the known samples in the database. The legal limit in almost all states is you must test only for identification purposes, for law enforcement purposes. But those terms are not defined. It doesn't say law enforcement purposes or law enforcement identification means only these junky identifiers. It could be knowing what the suspect looks like is a law enforcement identification purpose.

  • 11:26:26

    REHMJohn Butler, do you want to jump in here?

  • 11:26:31

    BUTLERYou know, one of things I think is important to realize is there's different levels of DNA that's being tested. And I compare it with my math analogy. I have -- you know, basic math is when you're doing single-source samples that go into a database. They're single-source, they're very easy to type, two plus two equals four. When doing sexual assault, you're doing algebraic equations, if you will. And when you get to these touch -- more complicated evidence, where you these statistics and these challenges, you're looking really at calculus.

  • 11:26:56

    BUTLERAnd so that -- the challenge that you have is that many times, labs are being prepared and trained very well to do algebra and basic math, but they have to really learn how to better do the calculus. We have to prepare proper exams, get ready for that kind of thing. So when we talk about DNA, sometimes we lump it all into all tests are equal. They're not. So we -- when we have a complex situation, we do have a calculus situation.

  • 11:27:19

    REHMMitch Morrissey, what about civil liberties here, and how does that enter into your own calculations?

  • 11:27:27

    MORRISSEYThat's always something you have to consider. If you're doing something, you know, you want to do it in a constitutional, legal manner. So you need to know what the law is, what the case law is around a particular -- a particular issue. We've already talked about abandoned DNA. Obviously that's a Fourth Amendment issue. If something's abandoned at a crime scene, there's no expectation of privacy, those types of issues.

  • 11:27:54

    MORRISSEYWhat I do as the elected district attorney of Denver, when there is case law that comes down around putting in, for instance, non-conclusive DNA results, that can be a problem because you don't have a statistic. I need to make sure my lawyers that are trying those cases understand that that's a potential issue where they could into a problem, if they're making improper arguments around DNA, those types of things.

  • 11:28:20

    MORRISSEYSo I think in the last week, I sent out two emails to my staff, to my lawyers, about being careful around DNA and the legal issues that can come with that, when you need a warrant, those types of things.

  • 11:28:30

    REHMAll right. Is it -- it is of concern to you, Mitch Morrissey, that apparently these databases have disproportionate numbers of African-American and Hispanic men in them?

  • 11:28:50

    MORRISSEYWell, that's true because of our criminal justice system and the way that the states have decided to populate the DNA databases based on criminal convictions, based on criminal arrests. There's an over-representation of people of color in our criminal justice system. Because of that, then the DNA database reflects that. If there had been another approach about how we populated these DNA databases, then that may not have been the case, but that is the case. That's a reality in the criminal justice system.

  • 11:29:26

    REHMAll right, Erin, do you want to...

  • 11:29:26

    MORRISSEYBut I think the system, you need to realize.

  • 11:29:29

    MURPHYI think that...

  • 11:29:29

    REHMHold on.

  • 11:29:29

    MORRISSEYThe system needs to be used.

  • 11:29:32

    REHMAll right.

  • 11:29:32

    MORRISSEYI mean, the fact that that's there, you have to realize it's there.

  • 11:29:37

    REHMAll right.

  • 11:29:37

    MORRISSEYBut you also have to realize there's a huge over-representation of victims of violent crime in this country that are people of color, and to not use this database to try to get leads to solve those cases would be an incredible injustice to those people.

  • 11:29:52

    REHMAll right, Erin?

  • 11:29:54

    MURPHYI think, you know, several things. One, race is a critical question for our criminal justice system generally. We're seeing that as a social movement now. And it is an important question for the DNA databases in particular. And I'll say several things about that. First, you know, the DNA databases are not, as Mitch said, they're not cobbled from abstract, you know, theories. They're cobbled from policies about who has to contribute to them, you know, compulsory rules about convicted offenders, arrestees, and we know that those, you know, practices don't map on demographically to the rate of even offending.

  • 11:30:30

    MURPHYSo I don't mean -- you know, we know that, for instance, in New York we had a huge debate because we know that the people, the number one crime of arrest for a long period of time in New York City was possession of marijuana. That crime is a crime that actually whites disproportionately a little bit higher than African-Americans, and yet overwhelmingly the people arrested for that crime were African-American.

  • 11:30:49

    MURPHYAnd so I think when you make these policies, you can't sort of assume away the discretion to arrest, the discretion in the criminal justice system to prosecute and convict people. And if you know anything about the criminal justice system, you know that violent crime, rape, murder and so forth, is a really small fraction. It's a large number of cases, but it's a small fraction of crime in our country, you know, what -- in terms of who's arrested and convicted, if you look at felony arrests, for instance, you're not going to see felony arrests, people convicted of felonies are 90 percent rapists and murderers.

  • 11:31:20

    MURPHYYou're going to see that they're, you know, 10 percent that. And there are huge percentages of drug crimes and other kinds of violent crime that have these racial patterns. And so I do think our databases reflect that.

  • 11:31:31

    REHMAnd reflect that unfairly in your view, Erin?

  • 11:31:35

    MURPHYI think so. I think they do unfortunately replicate the injustices in our system, the disproportionate representation of certain persons in our system. And then there's a lot of things that flow from that. Then when we use our databases, for instance, to do certain kinds of searches, like familiar searches as they're done in Colorado, then we're affecting communities of color in a different way than we're affecting white communities, for instance.

  • 11:32:00

    MURPHYOr when we talk about, you know, privacy questions of other kinds, of how we're going to use DNA, we're going to be affecting certain racial groups more than others.

  • 11:32:08

    REHMJohn Butler, is that of concern to you, as well?

  • 11:32:11

    BUTLERWell, I think as Mitch pointed out, and Erin echoed that, it's the criminal justice system in its entirety. And, you know, from a technical standpoint, samples are put in, and we don't really know -- on the database itself there's no record of what the race is or the ethnicity of the individual. It's just a profile. And so from the profile itself, you can't tell the ethnicity of an individual.

  • 11:32:35

    REHMBut how well do lawyers and juries and judges understand the statistics that are associated with DNA?

  • 11:32:44

    BUTLERWell, they don't. I mean, that's part of the challenge is that we need to bridge that gap in communication and help people be able to better understand what this information really is and what it isn't. What are the limits of the technique and how it's understood?

  • 11:32:57

    REHMDaniele, you presented evidence in court. How difficult is it to explain to juries what it all means?

  • 11:33:05

    PODINIIt can be very challenging. I think there's an expectation in the jury that DNA can solve everything, the famous "CSI" effect. And I don't have anything against "CSI." You know, in the span of an episode I've been from being a geek to being really cool. So I'm very happy about that. But at the same time, they created the excessive expectations in juries and investigators and prosecutors that DNA and other disciplines in forensic science can solve any kind of crime.

  • 11:33:41

    PODINISo the challenges of explaining these complex scientific concepts to a juror that doesn't necessarily have a Ph.D. or a college degree are challenging, and it's difficult.

  • 11:33:55

    REHMAnd you're listening to "The Diane Rehm Show." Erin, you wanted to jump in.

  • 11:34:01

    MURPHYYeah, I just would add, these challenge I think are becoming more pronounced. You heard reference from John and I think also from Mitch to the use of software to try and create statistics in these very complex DNA samples, and these software packages are really useful. They're an advance that can be, you know, helpful in creating meaning out of these very difficult samples.

  • 11:34:23

    MURPHYBut on the flip side, they require a very technical sophistication. They require the analyst to be able to understand exactly what they're putting in, the kind of choices they're making and how that might affect what they get out. And then when you take it to a jury, you know, essentially you're in a position potentially where you're telling a machine spit out this number, this number is the single most important and perhaps the only evidence convicting this person in the case, and I can't explain to how the machine came to that number, including that some of the software companies are not disclosing the way in which their machines create this number.

  • 11:34:53

    MURPHYAnd so you go to court, and the only person in the whole courtroom who knows how that number came to inculpate the defendant is the guy sitting on the stand who's got a for-profit interest in creating inculpatory information, and that's a real problem.

  • 11:35:06

    REHMSo Mitch, how do you deal with that?

  • 11:35:08

    MORRISSEYWell, that's just not the case and been my experience. I have never seen anyone charged with a serious crime on one of these complex, low statistics that we are seeing now with these complex mixtures. Primarily what we're seeing with the use of DNA is single-source samples, which John said is two plus two, or rape cases where we may have two different people's DNA there, but it's very clear who the major and minor component is. That's 99 percent or more of the work that's going on in the courtrooms.

  • 11:35:42

    MORRISSEYAnd then we get down into these complex mixtures, and I understand there's more and more of that, but there's a push from the court to have a statistical analysis for these complex issues, you can't put it into evidence in my state unless there is a statistic. But I'm not seeing people getting convicted of crimes like murder in my jurisdiction when one out of six people have a DNA profile from a complex mixture. The idea that that's the only evidence that would be presented in a case like that I think is ludicrous.

  • 11:36:13

    MORRISSEYI've never seen it in the 30 years of doing this. I've never seen it in the 30 -- in the 25 years of doing DNA evidence.

  • 11:36:22


  • 11:36:24

    MORRISSEYDNA evidence is a companion, usually, with all kinds of other evidence, fingerprints, eyewitness testimony, other circumstantial evidence. So, I mean, this idea that you've got this obscure, low profile that is somehow convicting somebody, I just -- that's not been my experience.

  • 11:36:45

    REHMAll right, Eric, do you want to comment?

  • 11:36:46

    MURPHYI'll just say quickly, we are definitely seeing it, and the fact that there are about 10 companies who are creating this software is a testament to the demand for the software. If it were true that it were never used anywhere, there would not be 10 companies making a business of it. And you can go to any one of their websites and see all the cases in which it's been admitted in evidence.

  • 11:37:05

    REHMErin Murphy, she's professor of law at NYU, author of the book "Inside The Cell: The Dark Side Of Forensic DNA." We'll take a short break here. When we come back, we'll open the phones, take your email. I look forward to speaking with you.

  • 11:40:01

    REHMAnd welcome back. We're talking about the growing use of DNA as evidence in various kinds of cases. We have an email from Paul, who says, "If DNA is becoming or is now an exact science, why do we keep hearing about cases where DNA pointed the finger at one individual, but years later, come to find out, that individual is not guilty, as the courts said?" Mitch Morrissey?

  • 11:40:43

    MORRISSEYWell, it's usually the opposite. On most of the cold case exonerations that I'm aware of in the United States, they're old convictions that pre-existed before DNA. Then the evidence is tested and DNA shows the individual was exonerated. So, you know, I'm not aware of a lot of cases where DNA actually was used to identify a perpetrator and then eventually it was found that -- there are some cases where the technology changed. But it's usually the opposite. It's usually somebody gets convicted through other means, and then DNA testing goes in and shows the person was actually innocent.

  • 11:41:23

    REHMAll right. Erin?

  • 11:41:26

    MURPHYI, you know, I think we are seeing that. There are a number of ways, as we've raised earlier in this conversation that you can have DNA results that unfortunately point the wrong direction. You can have inadvertent transfer, like we saw in a California case, where a man was suspected of a homicide based on swabbings from the fingers of the decedent. And it turned out he had spent the whole night in a detox unit of a hospital.

  • 11:41:46

    MURPHYAnd what happened was the paramedics who had responded to the crime scene had earlier treated him and that the item they put on the decedent fingers had transferred this man's DNA. So that's a good example of, you know, an inadvertent transfer. But we were able to detect that it wasn't, in fact, the right person. Or you see in examples of that, there are examples in my book of cases of transfer, that kind of contamination that happens in a crime lab because crime labs, even when they are, you know, following the best practices, are going to have those kinds of accidents.

  • 11:42:15

    MURPHYAnd you hope they are caught. We've seen -- when technology changes, we've seen old DNA that inculpated someone with retesting, you know, with more advanced testing show that that isn't, in fact, the person. So, you know, we have seen that. Is it the overwhelming number of cases involving DNA in our system? No. Thankfully, heavens no. But does it happen? Absolutely.

  • 11:42:33

    REHMBut do you have any idea the number of cases that have been overturned as a result of DNA?

  • 11:42:42

    MURPHYI think it's a really hard number to assess. And this is where -- one of the major points I hope to make with my book, is the need for greater accountability and transparency. Because the cases that we know of we know because there was objective evidence that showed there was a problem. But when you have a system of kind of lack of transparency, lack of accountability you really -- you're not gonna get as clear a picture of that. So I'll just give one suggestion of a beneficial thing we can do.

  • 11:43:08

    MURPHYJohn Butler, who's here in studio, has recommended that analysts use what he calls profile interpretation worksheets. And essentially it's just a worksheet that says here's what I did when I took apart this, here's what I found, here's the assumptions that I made, you know, here's what's there. It's an obvious thing for analysts to do, to just make clear all of their findings and their assumptions. And yet, that's not the universal standard at all.

  • 11:43:29

    MURPHYIn fact, we've seen analysts who refused to disclose times when there have been, you know, contrary findings that could be exculpatory to the defense. And yet, they haven't disclosed that. So there lots of basic accountability, transparency practices that both would improve the use of DNA and give us a better sense of what kind of errors are happening and with what frequency.

  • 11:43:49

    REHMJohn Butler?

  • 11:43:49

    BUTLERYeah, we actually had a conference this summer that NIST, National Institute of Standards and Technology sponsored, call the Error Management Conference. We brought in people from many -- 11 countries, over 400 people. And we talked about the issues with errors and the need to have more transparency and have ways to be able to address these things. So that's certainly something that needs to be done more, is to look more carefully at the details of how DNA testing is done.

  • 11:44:13


  • 11:44:14

    PODINIYes. And one of the points that Erin made about DNA transfer is very important to consider. The fact that DNA has been found at the crime scene, doesn't necessarily mean that the individual committed the crime. The methods are so sensitive now that we're able to pick up very, very low amounts of DNA and it can be transferred. Even if person A shakes person B's hand, and person B shakes another person's hand. You can find person A on person C. So there's -- an individual can act as a vector from one individual to an object.

  • 11:44:52

    REHMAll right. Here's another question for you, John Butler. "New research indicates a much higher percentage of people have more than one kind of DNA in their bodies. The technical term is chimerism. Can you explain that?"

  • 11:45:15

    BUTLERSo chimerism is a situation where you have not just one DNA typed through the entire body, but you may have a type from another individual in there. And so certainly in vitro fertilization, other techniques to try to, you know, make someone more fertile, often there's multiple embryos that can start. Those confuse sometimes. And then you can have another -- so basically, you can be both yourself and your sibling, if you will, in terms of the DNA.

  • 11:45:40

    BUTLERAnd there's been cases where that's happened. However, that's something that's more rare. That's not something that's gonna be a common situation. But as sensitivity improves, you can look lower and lower into the depths of the DNA testing that could be done, certainly chimerisms will be detected occasionally.

  • 11:45:56

    REHMAll right. To Lansing, Mich. Scotty, you're on the air.

  • 11:46:02

    SCOTTYHi, Diane. Thanks for taking my call. (caller)

  • 11:46:04


  • 11:46:05

    SCOTTYMy question is about the weight of DNA testing and, you know, the CSI effect. If most people think that DNA testing is the silver bullet and we want to get rid of the CSI effect, how much weight should DNA testing have in a case? Should it be a 99 percent, you know, weight when people hear yes, this is a match? Or should we say, well, no. We have to take in all pieces of evidence when we're considering this case? Thank you.

  • 11:46:40

    REHMMitch Morrissey?

  • 11:46:42

    MORRISSEYThat it -- what I see is that jurors do take in all the evidence and they do consider DNA when you have it. They consider all the other evidence. You know, I think that people discount the fact that DNA is used to exonerate thousands and thousands of suspects before someone's even charged. It's very cost effective for getting rid of good suspects before there's even a charge, before you got to a jury.

  • 11:47:07

    MORRISSEYI mean, yeah, as far as the weight of evidence goes, DNA is significant, but, you know, there's obviously other evidence there that could be presented or is presented. And it all goes together. This idea that people just, yeah, that they ignore all other evidence just has not been my experience.

  • 11:47:27


  • 11:47:28

    MORRISSEYAnd I've been preventing DNA since 1989.

  • 11:47:31

    PODINISo the -- to answer the caller, I would say that it depends on the case. The DNA is analyzed on the case, a profile is generated, a match is determined. And then a frequency of the profile in the population is determined, which -- and likelihood ratio is determined, which gives weight to this match. And so the weight is determined by the quality of the profile, by the number of regions that are analyzed and by the statistical calculation that is performed, which is based on the frequency of these regions in the population. So it's a case by case.

  • 11:48:11

    REHMBut Erin is concerned about those statistics.

  • 11:48:16

    MURPHYWell, I'll just add a couple things. I mean, I think it's absolutely right, it's a case by case thing. You know, you could have a very simple sexual assault case, for instance, where you have a large quantity of DNA, it's from an intimate sample that's unlikely to have arrived there by, you know, transfer, if there's no signs of contamination, etcetera, etcetera, that's something we can have a lot of confidence in.

  • 11:48:33

    MURPHYOn the other hand, you can have one of these touch mixtures, a very low quantity, where you worried about the reliability of the statistics that were produced. You may not trust the juror's ability to understand those statistics. You may worry a lawyer just used DNA and throws up their hand and pleads the case or, you know, thinks this is the same thing as the rape case I just described. And so I do think it's case by case.

  • 11:48:55

    MURPHYI want to say one other piece I think it's important. I think the exoneration cases have been critical in so many ways to help us understand the problems of forensics in our system. At the same time when it comes to DNA, I do think they've had an effect of kind of bolstering this reputation of DNA as infallible. Because we think if they're releasing people who've been convicted of crime, saying their innocent because of DNA, this must be a flawless technique.

  • 11:49:18

    MURPHYBut the problem is is the exoneration use of DNA is a little bit easier. It's not, you know, free from challenges also, but it's easier than inculpatory uses because you can have a very smaller…

  • 11:49:27


  • 11:49:27

    MURPHY…incomplete sample and…

  • 11:49:29


  • 11:49:29

    MURPHY…know for sure this is not the guy. As opposed to having a smaller incomplete sample and trying to conclude this is the guy, especially if you have match that works.

  • 11:49:35

    REHMAll right. Let's take a call from someone who has had direct experience. John, in Salem, Conn. You're on the air.

  • 11:49:48

    JOHNHello. Thank you. Yes, I'm working through a case with my son. It's been going on for eight years. The state is using junk science. And that's the simplest way to put it. One of the things that -- and I've heard your discussions before of DNA. People don't understand, in blood only about 3 to 5 percent of the blood, white blood cells, has DNA. Red blood cells, everything else has no DNA in it. So that's a starting point, it's very low.

  • 11:50:16

    JOHNThen when you put in an IV for the person, that even flushes it out even more. In this particular case, the state refused to give up the raw DNA data. And that's -- several of your people have said they don't know where it came from. We had to use a Freedom of Information Act and it took a year after the trial to get the raw DNA. At that point what we found is some of the DNA had a range scale of 0-90. Some of the DNA had a range scale of 0-4,800. Yet, it was all reported as the same level.

  • 11:50:51

    JOHNAlso in there we found that Dr. Nicholas Yang of Connecticut hand selected points, then re-ran data at different scales, force-fitting. He did not use a blind or double-blind type scientific approach. So he force fit data. This is the type of things that are going on. And unless all of the raw data is provided, none of this should be used in court.

  • 11:51:22

    REHMAll right. Daniele?

  • 11:51:23

    PODINIWell, I don't know the specifics of this case, of course, but what John pointed out is important. The analysts should review the data, the forensic data, the data from the forensic sample before looking at the references. Make, draw their conclusions based on that, and solely on that. And that data should then be reviewed independently by a different analyst that doesn't know the results that the first analyst obtained. And then should be compared to the evidence -- to the reference samples. So only then. And the conclusions that are drawn on the evidence cannot be changed.

  • 11:52:02

    REHMMitch, do you want to comment?

  • 11:52:05

    MORRISSEYYou know, I just don't know the facts of what they're talking about in Connecticut. And I have a practice of not commenting on other people's cases when I don't know what happened.

  • 11:52:15

    REHMAll right.

  • 11:52:15

    MORRISSEYWhat I can tell you is that when people -- when we file a case and people ask to see the raw data, they ask to see the procedures that were taken, they ask to see validation studies that have gone for years, instances of contamination, all of those things are made available for experts to review upon request, if that's what the defense team wants.

  • 11:52:41

    REHMAll right. And, Erin?

  • 11:52:42

    MURPHYYeah, I just, you know, I think Daniele makes a critical point about ways in which a supervisor or a lab can eliminate some of the biases we know can come into play, even inadvertently, not intentionally. Also, I just want to highlight one thing the caller pointed out, which is the discovery, it's called. The handing over of the raw material, the handing over of all of the associated information you would need to form an independent judgment of the evidence.

  • 11:53:04

    REHMWhy would he have had to use a FOIA to get that information?

  • 11:53:09

    MURPHYUnbelievably that is the practice in many jurisdictions. The National Commission happily, just recently, issued a recommendation, the beginning of which was, "The key values of honesty and openness are essential for science to progress and this is no less true when the science is intended to be utilized in the legal process."

  • 11:53:23

    MURPHYAnd you might think, why in 2015 does the National Commission have to write a sentence like that? Why is not obvious that we should be fully disclosing science? And yet, even in my own New York jurisdiction they don't hand over raw data on a regular basis.

  • 11:53:35

    REHMAnd you're listening to "The Diane Rehm Show." Why is that?

  • 11:53:42

    BUTLERWhy don't they disclose more information?

  • 11:53:43


  • 11:53:44

    BUTLERI mean that's part -- part of it is culture of how labs are set up and versus the culture of science, of wanting to share stuff. I think a lot of labs would be happy to share data, just the environment that are in, sometimes they're not allowed to. And so trying to create policies in place -- Erin mentioned the National Commission on Forensic Science. They just discussed discovery policies and things like that.

  • 11:54:05

    REHMWe have a tweet from Matthew, who's saying, "Who provides oversight and questions for labs? Is there an internal affairs department for them?" Daniele?

  • 11:54:21

    PODINICrime labs are accredited by the Association of Crime Lab Directors DNA Analysis Board, which is made by forensic scientists. And they have petitioners that validate, that inspect laboratories periodically to determine whether they're following the guidelines that they should follow.

  • 11:54:51


  • 11:54:52

    MURPHYThat is true. I think we still see that there's major shortcomings. That accreditation body has been accrediting every single lab that's gone through a major scandal. So we know it's not working the way it should. And I'll just give some comparison. The clinical laboratories have to follow a federal statute that requires that they are inspected, you know, the inspection happens quarterly, it could happen, you know, twice a year, if it's a very complex process. Their certifications only last two years. There's certification requirements that allows the tests.

  • 11:55:22

    MURPHYThere are limits on the number of samples they're allowed to run so that people aren't, you know, pushed to do more than they can. That is how you get medical laboratory testing done, if you want to be, you know, diagnosed with flu or what have you. In a criminal laboratory system, we've not had mandatory accreditation, generally. The DNA database, the national database requires accreditation, but they just defer to these organizations. They don't do their own independent audit.

  • 11:55:44

    MURPHYThose organizations aren't rigorous. They're coming in, they're giving notice, it's not a spot check. They usually just ask for the, you know, entity to produce files. They do a paper review. There's no reanalysis. There's not the kind of spontaneous, unexpected inspection that really would recover flaws. And in New York, for instance, we have 24,000 restaurants. You know how we make sure our sandwiches aren't corroded?

  • 11:56:05

    MURPHYWe do unannounced spot checks. And that's how we know the roaches really aren't there or the rice -- mice really aren't there. And I think anyone will tell you, you make your house nicer when you know someone's coming over. And if you know you're only gonna have a paper review you're not gonna get the real, you know, people who are doing things they're not supposed to do or who maybe aren't competent to do the job they were assigned to do. So we could shore up that process tremendously.

  • 11:56:26

    MURPHYAnd I'll just add one more thing, the FBI also reviews databases to make sure they comply with the uploading rules. The rules about what you can put in the database. And that they do do. They pull the case and they kind of reanalyze it, if you will. And there they find error. They found about an average of 6 percent error rate for uploads. And that tells you, I think, that when you do that kind of checking, you are more likely to find mistakes. And over time I think you've seen some of those mistakes diminish as people learn from the auditing process.

  • 11:56:55

    REHMVery interesting. Sounds as though there's a lot to learn here. And a lot more oversight needed. Erin Murphy is professor at NYU Law School, author of "Inside the Cell: The Dark Side of Forensic DNA." Daniele Podini is professor at George Washington University. John Butler is at the National Institute for Standards and Technology. Mitch Morrissey is district attorney of Denver, Colo. Thanks for listening, all. I'm Diane Rehm.

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