Category Archives: DNA

Houston in the Blind

Blind studies and procedures are the gold standard of evaluating the quality and reliability of scientific results. Unfortunately, this has long been lacking in forensic science. Fortunately, strides are being made to introduce blind testing to forensics, most notably in the Houston Forensic Science Center (HFSC).

Currently, forensic scientists are tested periodically on their knowledge and ability through proficiency tests. However, scientists typically are aware they are completing a proficiency test and not case work. This allows for the Hawthorne effect to play a role in the testing, or the phenomena of a person behaving differently when they know they are being observed. Blind testing in forensic science will allow for blind samples to be included with case work in a manner that scientists cannot distinguish between a blind and a real case. This will help distinguish whether or not a laboratory adheres to guidelines and whether best practices are used in a day-to-day setting, as opposed to simply during an anticipated exam.

This article describes the efforts of Dr. Peter Stout, the HFSC’s chief executive officer (and former member of the NC Forensic Science Advisory Board), to implement a “blinds program.” So far, 329 blind samples have been integrated into normal casework in the firearms, toxicology, DNA, fingerprint, and digital forensic sections of the lab. In 2018, the lab plans to grow the program to 800 blind tests per year, or 5 percent of the lab’s workload.

Disguising a blind as a case sample is not a simple task, as the Forensic Magazine article describes. In addition to the challenge of creating a case submission that appears authentic, another particularly challenging aspect has been determining whether the blind samples could be searched in databases like AFIS, NIBIN, and CODIS.

At the HFSC, no errors have yet been reported in the testing of a blind. Use of blind tests will allow the lab to begin reporting error rates and confidence intervals, which will strengthen the testimony of analysts and allow them to answer questions about reliability of their work.

If you’ve made it this far in the post and are still wondering about the title, “Houston, in the blind” refers to a phrase used by astronauts when they aren’t receiving any response from ground control. The phrase indicates that they will continue to communicate, not knowing if ground control is receiving their message. My hope for forensic science is that communications about blind testing will not be “in the blind.”




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Happy National DNA Day!

If you handle cases involving DNA evidence and don’t know the story of Lukis Anderson, stop what you are doing and take a few minutes to observe National DNA Day by reading this great article by Katie Worth of The Marshall Project.

Mr. Anderson was a homeless man living in San Jose, CA whose DNA was found on the fingernail of murder victim Raveesh Kumra. As a result of the DNA match, Mr. Anderson was charged with murder and spent several months in jail on that charge before the innocent explanation was uncovered for his DNA being on a murder victim who was unknown to him.

Both Mr. Anderson and Mr. Kumra were attended to by the same team of paramedics on the night of the crime. After Mr. Anderson was transported to the hospital, the paramedics responded to the scene at Mr. Kumra’s home. Had Mr. Anderson not had an airtight alibi established in his medical records, showing he was in the hospital at the time that Mr. Kumra was murdered, it is likely his case would have had an outcome other than dismissal.

The Marshall Project article explains the phenomenon of DNA transfer that Mr. Anderson’s case illustrates. There has been scientific research on DNA transfer showing that 1 in 5 of us walk around with someone else’s DNA under our fingernails. People shed 50 million skin cells a day, and research has demonstrated how easy it is for DNA to be transferred to an object that a person has never touched. Because techniques for analyzing DNA have become more and more sensitive, it is possible now to develop a profile with a small number of cells – cells which are easily transferred.

If you’d like additional information about DNA transfer or the challenges of interpreting very small amounts of DNA, please contact me ( and I’d be happy to discuss further and share some articles with you.



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Royal Society Forensic Primers

Both experienced and newer attorneys should be aware of two primers, released by The Royal Society, on forensic DNA analysis and forensic gait analysis, available here. Although these reports were intended for use by courts in the UK, they provide important information for attorneys in the United States. This blog post intends to give a brief overview of notable sections of the primers.

Within the DNA analysis primer, attorneys may find the information on Y chromosome DNA analysis and mitochondrial DNA analysis helpful. Y chromosome DNA analysis (p. 11) is a technique that is useful when there is a mix of male and female DNA, such as in sexual assault cases. Mitochondrial DNA analysis could be helpful in cases where DNA evidence is small or breaking down, for example in a cold case or post-conviction case (p.12). Mitochondrial DNA is present in a cell greater amounts than nuclear DNA. Mitochondrial DNA is passed down from mother to child, and is nearly identical in maternal relatives, and the Y chromosome is nearly identical in paternal relatives, so it should be noted there are greater odds of multiple people matching a mitochondrial or Y-STR profile by chance or due to relatedness.

Another section of the primer that may be of interest is the discussion of contamination (p.32) and DNA transfer (p. 46). Contamination is “the introduction of DNA, or biological material containing DNA, to a sample after a (trained) responsible official has control or the crime scene.” (p.32). To prevent contamination, precautions should be taken such as following the international standard for DNA-free items.

The primer notes that once there is an appropriately-handled DNA sample, the forensic scientist should interpret the DNA evidence sample first, document the findings, and then the scientist should compare it to known samples of DNA (p.34). The process should be done in that order to avoid confirmation bias. The primer also contains an explanation of DNA statistics that may be useful for attorneys.

Lastly, The Royal Society also released a notable primer on forensic gait analysis.  Forensic gait analysis evaluates a person’s manner and mannerisms in their walk and compares it to a recorded video to determine if it is the same walk and as such the same person. This type of evidence is more common in the UK where video surveillance is more prevalent. However, the primer’s assessment of this type of evidence is interesting as the assessment could be applied to other novel techniques. While the primer notes that there are accepted clinical uses for gait analysis by various types of health professionals, that doesn’t mean that the technique has a validated forensic use. The primer finds that there is not enough scientific evidence to determine one’s identity solely from their walk because it is not certain that people don’t share walk patterns, there is no known error rate or standardized methodology, and there are no published black-box studies on the technique’s reliability and repeatability.


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NIST urges caution in use of likelihood ratio

The National Institute of Standards and Technology (NIST) released an article last week calling into question the use of the likelihood ratio to present evidence in court. NIST states that there is uncertainty about the appropriate use of the likelihood ratio. An expert’s subjective opinion may affect the calculation of the likelihood ratio, potentially distorting the evidence. More information is available here.

Attorneys who see a likelihood ratio in a lab report should consider the NIST report and  investigate further prior to trial. Many labs are moving toward implementation of the likelihood ratio for interpretation of DNA analysis. To my knowledge, the NC State Crime Laboratory and the Charlotte-Mecklenburg Police Department do not employ the likelihood ratio in their interpretations of DNA evidence, though it could be adopted at some point in the future. The likelihood ratio is used by some private laboratories, such as NMS Laboratories.

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New Research on “Touch” DNA

As the sensitivity of DNA analysis increases, scientists are able to develop profiles from ever-smaller samples of DNA. This has lead to testing of a wider array of samples collected from crime scenes, including window panes, bullets, hats and other clothing, cigarette butts, and many other items.

Attorneys sometimes ask me about the likelihood of obtaining a useful DNA profile from certain items of evidence. A study from six European forensic laboratories may give some idea of how likely it is to find a DNA profile on items commonly found at crime scenes. This article contains an interesting chart that lists the item and the likelihood of finding a full profile, usable partial profile, possibly usable partial profile, or no profile. It seems best to use this type of information as a rough guide, but it is interesting nonetheless.

It is important to keep in mind that as labs are able to analyze smaller amounts of DNA, the possibility of developing partial profiles and complex DNA mixtures increases. Where very small amounts of DNA are involved, the sample may have been deposited by secondary transfer. Here’s an interesting article on secondary transfer and “touch” DNA.

Attorneys should be aware that forensic laboratories may have case submission guidelines that limit the number and type of items that may be tested by the lab. To understand why and how an item was tested (or not), it is important to read the lab’s policies and guidelines. Here is a link to the North Carolina State Crime Lab’s Evidence Guide. There is information about Touch DNA testing on p. 52.


Filed under Crime Labs, Crime Scene, DNA

Familial DNA Testing

by Emily Zvejnieks

Familial DNA testing, an innovative yet highly controversial technique, is being used in several states. This blog post will provide an explanation of what familial DNA testing entails and briefly discuss its Fourth Amendment implications.

In standard DNA testing where there is an unknown sample, that unknown sample may be compared against samples in the Combined DNA Information System (CODIS), an index maintained by the FBI. The index is made up of samples of convicted offenders and individuals who have been arrested or charged with certain crimes but not yet convicted. Traditionally, the unknown sample is compared against known samples in the database, looking for an exact match.

In situations where an unknown sample exists but a search of an existing DNA database returns no exact matches, it is possible to conduct a search to identify potential relatives of the alleged perpetrator. This process is called familial DNA testing. The actual process is a low-stringency search, which produces inexact matches. The search is based on the idea that those closely related to each other share more genetic data than those not closely related.

There are two pending U.S. cases currently in the spotlight where defendants were identified as a result of familial DNA testing in California and Wisconsin. Lonnie Franklin, Jr., also known as the alleged “Grim Sleeper” serial killer, is charged with several counts of murder for crimes that occurred in Los Angeles in the 1980s and 2000s. In that case, authorities obtained the perpetrator’s DNA from various crime scenes. After running the DNA through the offender database with no exact matches and no other suspects, the sample was submitted for familial searching, and the search rendered a result of a potential first-degree family member. Detectives then determined that Lonnie Franklin, Jr., the father of the person whose DNA sample was in the database, lived in close proximity to most of the crime scenes.  An undercover officer then followed Franklin to a local pizza joint and, after Franklin was finished with his plate, collected his plate, pizza, and utensils. After testing DNA obtained from his leftovers, authorities matched the unknown sample to Franklin. Franklin has since been charged with ten counts of murder and one count of attempted murder, and his cases are pending.

Wisconsin recently used familial DNA testing for the first time. The case involves pending sexual assault charges against Michael L. Dixon.  A series of similar rapes that occurred between 2008 and 2012 in Milwaukee remained unsolved until a familial DNA search was performed using the perpetrator samples from the crime scenes. Using familial DNA testing, there were two close matches. Upon further investigation, it was determined that one of those matches did not have any male first-degree relatives, so that possible match was eliminated. The other close match did have a brother: Michael L. Dixon, who had been found not guilty of a 2012 rape with similar facts to the unsolved rapes. Wisconsin authorities had Dixon’s DNA sample from his arrest on the 2012 charges, but his DNA was never added to CODIS since he was not convicted. The perpetrator’s DNA from the unsolved rapes and Dixon’s DNA were an exact match. Dixon now awaits trial for first and second degree sexual assaults.

The Innocence Project opposed the use of familial DNA testing in a February 2013 position paper.  Interestingly, California implements many of the safeguards the Innocence Project suggests regarding admissibility of evidence procured through familial DNA testing. Michael Chamberlain, Deputy Attorney General of the California Department of Justice, wrote an article published by the American Bar Association in 2012 that lays out familial DNA testing use and practice.  California uses its own software called the “ratiometer.” After coming up with 150-200 possible close matches, the ratiometer runs a Y-STR test, which analyzes the Y chromosome only to determine whether there is a matching Y-STR profile. If Y-STR profiles match, that indicates there is a paternal relationship. Because the California process uses the Y-STR test, familial DNA testing cannot be used for females and also does not identify half-brothers who share the same mother.

Fourth Amendment implications of familial DNA testing are mind-boggling.  On one hand, we know that a defendant does not have a Fourth Amendment claim when his or her privacy interests were not violated.  Many of the samples entered into CODIS belong to convicted felons who, according to our justice system, gave up some privacy interests by way of their actions.  Familial DNA testing is a search of those samples.

On the other hand, the reason that there is no exact match in the CODIS database and familial DNA testing is being done is because the suspected perpetrator is not a convicted felon and thus his or her privacy rights have not been compromised.  Each person shares DNA with his or her parents, siblings, and children.  If one of them has given a sample due to being a convicted felon, or even gives a sample voluntarily, then their relatives’ DNA can be analyzed as well.

Arguably, familial DNA searching falls under the “technology not in general public use,” as discussed in Kyllo v. United States. In Kyllo, SCOTUS held that a thermal imaging device used to determine excess amounts of heat inside a private residence was a search as the technology employed was not in general public use.  Kyllo, 533. U.S. 27 (2001). Similarly, DNA searching is a technology not in general public use, and it could be argued that familial DNA testing is a search requiring a warrant – otherwise it would be a way for the government to get around Fourth Amendment protections of a person whose family member’s DNA is in a database.

Another concern with the use of familial searching is that it will create suspects out of innocent people simply because they are related to someone whose DNA is in a database and their relative’s DNA is similar to DNA found at a crime scene. Because of the racial makeup of the existing DNA databases, people of color will be disproportionately impacted. Innocent citizens will become subjects of police investigation, and will bear the privacy, emotional, economic, and liberty costs associated with being investigated for a crime.

As familial DNA searching becomes more widely used in the United States, it will be interesting to see what North Carolina as well as the Supreme Court of the United States decide on its use and admissibility. To date, the only known case where this technique has been used in North Carolina is the Darryl Hunt case. Certainly any jurisdiction choosing to perform familial DNA testing should implement stringent requirements for its use. For more information, this website offers a four-part webinar series on familial DNA testing.

Other Sources:

42 U.S.C. 14132.

Kyllo v. U.S., 533 U.S. 27 (2001).

Bruce Vielmetti, First use of Familial DNA test leads to charges in serial sex assaults, Milw. J. & Sent., July 11, 2014,

Chamberlain, Michael, Familial DNA Searching: A Proponent’s Perspective, Crim. Just., Volume 27, Number 1, Spring 2012.

FBI, Familial Searching,

Global Justice Information Sharing Initiative, An Introduction to Familial DNA Searching for State, Local, and Tribal Justice Agencies: Issues for Consideration,–Local–and-Tribal-Justice-Agencies.

Kim, J., Danny Mammo, Marni B. Siegel, and Sara H. Katsanis, Policy Implications for Familial Searching, Investig. Genet., November, 1, 2011.

Symposium, Family Ties:  The Use of DNA Offender Databases to Catch Offenders’ Kin, 34 J.L. Med. & Ethics 248 (2006).

Weiss, Lindsey. All in the Family: A Fourth Amendment Analysis of Familial Searching.  The Selected Works of Lindsey Weiss.  Available at:

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Changes to Protocols for DNA Interpretation

Recently, the State Crime Lab has undergone several rounds of changes and updates to their protocols and standard operating procedures (SOPs) for the analysis and interpretation of DNA evidence. Attorneys should be aware of these changes and that only cases worked on or after the effective date will be subject to the new policies.  Previously-worked cases will not be reevaluated by the Lab to determine whether the new policies would have resulted in any change(s) to the conclusions drawn. Three changes are worth noting in the most recent update (Procedure for Casework DNA Interpretation, Effective Date: 03/08/2013).

First, the Lab has changed their Analytical Threshold (also known as the detection threshold) from 75 RFUs to 50 RFUs. This threshold is similar to a cutoff value and is determined empirically by the lab through internal validation studies. In general, any allelic peaks in a DNA profile (as seen on an electropherogram) that pass that threshold are considered to be true alleles or artifacts and not background noise. Under previous protocols, peaks below 75 RFUs were considered to be below detection but were sometimes evaluated for the potential exclusion of individuals. By lowering the detection limit to 50 RFUs, the lab can interpret more information from low quality samples and/or mixtures where minor contributor(s) is/are present.

Second, in accordance with national guidelines that have been in place since 2010, the Lab has implemented another threshold known as the Stochastic Threshold. In essence, this threshold defines another cutoff value that is higher than the Analytical Threshold and provides the analyst with a zone of uncertainty in the DNA analysis data. This threshold (currently set at 200 RFUs) is also determined by the Lab through internal validations. Allelic peaks that pass the detection threshold but fall below the stochastic threshold (above 50 RFUs and below 200 RFUs) are said to be in Stochastic Effect, which is another term that refers to the technically-induced random loss of allelic data from a given DNA profile (also known as allelic dropout). Stochastic Effect is often caused by low DNA quantity and/or quality in a given sample.  For rendering interpretation from mixture profiles in particular, the Lab will no longer include allelic peaks that are in stochastic effect in their statistical calculations. (See Procedure for Statistical Calculations, Effective Date: 08/08/2013)

Third, the Lab has implemented a new empirically-derived value for what is known as allelic imbalance, a term that defines whether DNA alleles at a given marker/locus are representative of one or more individuals. This value is calculated by dividing the RFU value of the lower peak by the RFU value of the higher peak and expressing the number as a percent. After using a value of 50% for the past 5 years, the Lab has now implemented a new value of 65%. Alleles that are 65% (or higher) of RFU value from each other are said to be balanced (indicative of a single contributor).  If that percentage is lower than 65%, then there is an indication of allelic imbalance which plays a significant role in the interpretation of mixture profiles.

It is worth noting that the Lab has implemented a flow chart to be utilized by the analysts for DNA profile comparisons and interpretations (See Procedure for Casework DNA Interpretation, Effective Date: 03/08/2013, p. 10) and that the new SOPs reflect the Lab’s adoption of newer-generation kits for forensic DNA testing.  The three major changes described above can have a significant impact on the interpretation of DNA evidence and the overall conclusions reached by the Lab analyst in the course of analyzing evidence samples in general, and mixture/partial profiles in particular. Cases analyzed on or after March 8, 2013, will follow the new procedures. Cases analyzed previously will follow the older procedures and new conclusions will not be rendered on cases analyzed under the old procedures.  Defense counsel are encouraged to do further research or seek the assistance of a DNA expert to evaluate whether those changes (and other modifications to the SOPs) have a bearing on their cases.

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