Monthly Archives: September 2011

DNA Mixture Analysis – Is It Subjective or Objective?

DNA is often regarded as the gold standard of forensic science because of its purported objectivity, which makes it immune to subjectivity and bias. The National Academy of Sciences 2009 Report, Strengthening Forensic Science in the United States: A Path Forward even concluded that “[w]ith the exception of nuclear DNA analysis, . . . no forensic method has been rigorously shown to have the capacity to consistently, and with a high degree of certainty, demonstrate a connection between evidence and a specific individual or source.” (See p. 7.)

If it were truly objective, contextual information would not affect DNA analysis. In reality, however, when human examiners analyze complex DNA mixtures, the interpretations may be based on subjective judgments and may be influenced by contextual information to fit existing beliefs and expectations.

A recent study by Itiel E. Dror and Greg Hampikian, published in the journal Science and Justice, examined the effect of contextual information on DNA mixture interpretation. The study involved a DNA mixture analysis from a gang rape case in Georgia, where the case analyst had received contextual case information. The researchers then presented the same DNA evidence, without the contextual information, to seventeen independent DNA expert analysts.

In the actual case, one assailant agreed to testify against the other suspects in return for a lighter sentence. According to the Georgia rules of evidence, however, the assailant’s testimony was admissible only if the prosecution offered corroborating evidence. Only the DNA evidence provided the needed corroborating evidence. In the case, the analysts determined that the suspects—including Suspect 3, the primary suspect—could not be excluded from being contributors to the mixture. The analysts knew that without this determination, the informant’s testimony would have been disallowed.

When the researchers presented the original DNA evidence to seventeen independent analysts without the contextual information, with respect to Suspect 3, the independent analysts reached varied results: one concluded that Suspect 3 could not be excluded; four found the analysis inconclusive; and twelve excluded Suspect 3.

This result indicates that subjectivity may be present in purportedly objective DNA mixture analysis. Further, the varied conclusions by the analysts indicate that consistent and reproducible analysis of complex DNA mixtures may not always be possible.

Other DNA interpretation studies have been conducted of several laboratories by Dr. John M. Butler of the NIST laboratories. His studies raise similar issues, including questions about the differing statistical results produced by labs analyzing the same DNA mixture.

The Scientific Working Group on DNA Analysis Methods (known as SWGDAM) acknowledged in their publication (Interpretation Guidelines for Autosomal STR Typing by Forensic DNA Testing Laboratories, 2010) that “[d]ue to the multiplicity of forensic sample types and the potential complexity of DNA typing results, it is impractical and infeasible to cover every aspect of DNA interpretation by a preset rule,” thereby keeping the door open for subjective interpretation by the DNA analyst. This door is also open for knowledgeable experts to challenge interpretation of that data, particularly when it comes to the most difficult DNA samples to interpret, Low Copy Number (LCN) mixtures.

Anand Patel, UNC Law Student and NC State University Ph.D. Candidate contributed to this post.

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Update to “Freedom on the line for two North Carolina men”

A three-judge panel in Asheville ruled today that Kenneth Kagonyera and Robert Wilcoxson are innocent. The men who spent ten years in prison were exonerated by the judges’ ruling. This case which involved DNA testing that pointed to another suspect is the third case that has been heard by the N.C. Innocence Inquiry Commission and the second to result in an exoneration.

See the Asheville Citizen-Times for additional coverage.

Read previous post here.

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Warning about SBI DNA Reports

By Mark Rabil

Have you been given a report from the SBI Lab (now the State Crime Lab) that says the results of DNA testing are “inconclusive”?  Well, you should not necessarily believe it. The Tamera Bean noncapital murder case that was tried in Asheboro this month is a case in point. Defense Attorney David Botchin did a great job of doggedly pursuing the records in that case. This was a self-defense case in which the State contended the female defendant shot her boyfriend and staged the crime scene. In discovery, the SBI gave the DA and the DA gave the defense a report that said DNA testing on one of the shells was “inconclusive.” That was flat wrong: the defendant was excluded and the decedent was likely included. Read on to see why you cannot take the word of these lab reports.

It turns out three reports were written about the same SBI DNA testing in this case: the first report in 5/09 said defendant excluded as source of DNA; the second report in 6/09 changed the conclusion and said the results were “inconclusive” (the internal SBI lab “reviewer” made the analyst change the report, improperly); and the third report in 8/11 said defendant excluded. In the third report that was ordered by the court, the lab also added some language about how the sample was insufficient to submit to CODIS, a fact not in the first report, and intended to help the prosecution minimize the effect of the new report.

The State Crime Lab interpretation guidelines have gone through many revisions in recent years regarding the interpretation of mixtures and the reporting of inconclusives. (For the Crime Lab’s Interpretation Guidelines, you can visit the NCDOJ website or the NCIDS website or contact Sarah Rackley for assistance in locating the relevant procedures.) Counsel must remain alert to reporting language, however. According to the Ombudsman’s Report, the Crime Lab policy is that testimony should be based on the standards in effect when the testing was conducted, not the current standards (see p. 25). From the Bean case it isn’t clear whether analysts will identify whether the report was prepared according to the old protocols or the new ones. We also don’t know how many times a false inconclusive has gone misreported and undetected in other DNA cases or whether it is still happening in current cases. If you are working on a case where you think a false inconclusive may have been reported, contact IDS’s Forensic Resource Counsel (

Editor’s note:

Click here to read Mark Rabil’s August 29 guest column on the Bean case in the Winston-Salem Journal, as well as Judge Joseph John’s response and David Botchin’s response to the column.

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Freedom on the line for two North Carolina men

By Charlotte Stewart, UNC Law Student

This week a three-judge panel, formed as part of the N.C. Innocence Inquiry Commission process, is hearing a case which could exonerate two North Carolina men of murder convictions.

Kenneth Kagonyera and Robert Wilcoxson were convicted of the murder of Walter Rodney Bowman in 2000 in Buncombe County. Last Tuesday, however, a DNA analyst gave testimony regarding evidence found near the crime scene indicating that Kagonyera and Wilcoxson may not have been involved in the crime.

The DNA was found in saliva samples taken from bandanas that may have been used in the robbery that led to Bowman’s murder. The DNA did not match that of any of the six men originally investigated for the crime, but it did match that of another man, currently in prison, who was not originally charged with the crime.

In 2003, inmate Bradford Sumney was implicated by another prisoner in Bowman’s slaying and in 2007, there was a hit in the state’s CODIS database showing a match between the DNA sample from the bandanas and Sumney’s DNA. The DNA analyst who discovered the match testified that he sent notice to the Sheriff’s Office and the District Attorney’s Office that a match had been made to someone other than the two men convicted of the crime. However, according to the Innocence Commission investigation, no action was taken.

Kagonyera and Wilcoxson, currently represented by attorneys Noell Tin and Chris Fialko of Charlotte, initially maintained their innocence, but later pleaded guilty to the crime to avoid the death penalty.

It may take over a week for the panel to hear all of the relevant testimony, after which the judges will vote on whether to overturn the convictions, which requires a unanimous vote among the three judges.

The N.C. Innocence Inquiry Commission was formed in 2006 to investigate cases that may have ended in wrongful convictions and is the first of its kind in the country.

To follow continuing coverage of the hearing in the Asheville Citizen-Times, click here.

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Measurement Uncertainty

Any scientific measurement has some error associated with it. The concept of “measurement uncertainty” means that for even the most carefully performed measurement, the value of the thing being measured can never be known exactly – only an estimated value can be given.

Measurement uncertainty and error rates can come into play in forensic science whenever a numerical measurement is made, for example with blood or breath alcohol levels or even in measurements such as IQ scores.

In recent cases, courts have held that a calculation of uncertainty or error rate must be reported in order for blood alcohol measurements to be admissible. I’ve prepared a website with articles explaining this topic, motions and opinions from recent cases. Challenging the admissibility of a measurement where no error rate is given may seem most relevant in a DWI case where a BAC of .08 is reported, but it can also be used to strengthen other challenges regarding the reliability of forensic evidence. Attorneys should ask the lab prior to trial about the lab’s calculation of error rates and should expect that chemical analysts will be familiar with the concept given the attention it is currently receiving in the forensic community.

Recent reports and model lab standards support the use of error rates. ISO 17025 is an international standard for testing and calibration of laboratories and is the accreditation standard that the State Crime Lab is currently working to achieve. The Drug Chemistry Section of the Crime Lab has said it is already operating under some ISO standards. ISO standard 5.4.6 requires labs to estimate uncertainty of measurements.

Additional support for requiring measurement uncertainty to be calculated comes from the 2009 Strengthening Forensic Science in the United States: A Path Forward which states “[f]ew forensic science methods have developed adequate measures of the accuracy of inferences made by forensic scientists. All results for every forensic science method should indicate the uncertainty in the measurements that are made, and studies must be conducted that enable the estimation of those values.” (See p. 184.)

If you have questions about whether you can challenge measurement uncertainty in your case, let me know!

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CODIS: Combined DNA Index System

By Sarah Rackley
Edited by Dr. Maher Noureddine, forensic DNA expert

Note: Where State Crime Lab policies and procedures are referenced, I have cited to the most recent version that I have access to.

What it is:
CODIS (Combined DNA Index System) is the FBI’s program that allows forensic DNA laboratories to create and search databases of DNA profiles. The federal DNA Identification Act of 1994 authorized the FBI to create CODIS and set national standards for forensic DNA testing. CODIS became fully operational in 1998. CODIS databases exist at the local (LDIS), state (SDIS), and national levels (NDIS). This tiered architecture allows crime laboratories to control their own data, enabling each laboratory to decide which profiles it will share with the rest of the country (Source:,

How it is used:
CODIS contains an index of convicted offender and arrestee profiles. These profiles are developed from biological samples submitted when an individual is arrested for or convicted of statutorily specified crimes. (See Crime Lab procedures for CODIS and DNA Database Procedures.) Each state has different qualifying offenses, and there are requirements for entering the profiles into the local, state, or national database. (See G.S. 15A-266)

When biological evidence is collected from a crime scene or victim, a DNA profile of a suspect may be developed. This “forensic unknown profile” can be compared to profiles in the convicted offender and arrestee index. Regular searches are conducted of all DNA profiles in the National DNA Index System (NDIS) and resulting profile matches are automatically returned to laboratories that submitted them.

If there is a computer-identified “match” or “offender hit,” the Crime Lab initiates procedures to obtain a new DNA sample from the suspect and perform  DNA analysis in the lab to confirm the match. If you have a case where a CODIS hit was made, it is important to read Section 6 of the Crime Lab Procedures to ensure that the correct reviews and analysis has occurred.

Considerations if you have a CODIS cold hit case:

  • Is there a direct or reasonable correlation between the forensic sample that was collected from the scene and the crime itself? What are the chances that the sample belongs to a bystander, unrelated to the crime? This is especially important if the sample was developed as a “Touch DNA” sample. Using new technologies, minute amounts of genetic material can now be used to generate a profile that is suitable for CODIS.
  • How was the “forensic unknown profile” from the crime scene entered into CODIS? Consider possible sample mix up, contamination, and interpretation problems that could have occurred when the sample was entered. Who was the analyst who entered the sample? Some of the analysts who entered samples in the early 2000s are no longer employed by the State Crime Lab or were cited in the Swecker report, which raised concerns about the reliability of Crime Lab work.
  • How and why was the DNA sample collected from your client? Are there grounds to challenge that collection? If your client’s sample was in the database from a collection in NC, was the qualifying conviction or arrest pursuant to G.S. 15A-266.3?
  • Have you received the lab report from the Crime Lab’s analysis of the database “match?”
  • Finally, consider the standard questions you would ask regarding DNA analysis: How many loci match? What is the statistical significance of the “match”? (See this LA Times article.) How was that statistical significance calculated? (See this research on the probability of an erroneous attribution in “cold hit” cases) How did cognitive bias affect the analysis?

Motions practice:
A great resource for motions you may consider filing in CODIS cold hit cases is PocketExpert Consulting, LLC. This website has sample motions including the following challenges: when DNA has been taken from a client who has not committed a qualifying offense, the taking of DNA from a parolee, the statistical significance of the purported “cold hit,” the unreliability of a 9+ loci match, and CODIS vulnerabilities.

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