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  Home -> Resources

One DNA Test... Many Interpretations... Reasonable Doubt?

By Julie Heinig, Ph.D.
July 2, 2007

Each attorney has different needs and varying understandings of DNA testing and interpretation. Some do not know much about DNA, while others are very familiar with DNA testing and laboratory procedure. Forensic services are available to meet the needs of clients across the spectrum.

The following scenarios depict three different situations that require three different approaches from DNA experts.

Scenario A: "I'm new to the DNA testing field."
For those attorneys who have never been involved with a DNA case, their first one can be quite daunting. From the acronyms (i.e. PCR, STR, ASCLD/LAB, CODIS), to the statistics, to the terms (i.e. mixtures, partials, minor alleles, loci), there is a lot to know and understand. A DNA report may state that John Doe's DNA profile is consistent with evidence and that he can't be excluded as a contributor. The probability of an unrelated individual having the same profile as that on the evidence is 1 in 40,000,000,000,000,000 (or 40 quadrillion) individuals. The questions that may follow are often: Is DNA infallible? Was a mistake made? Is the evidence probative? Where does this statistic come from? How do we know what the source of the DNA is? What do I ask during cross? This is where it all begins! Case review and consultation can answer those questions and help prepare the attorney for the case.

Scenario B: "DNA testing didn't clarify my case... or did it?"
In some cases, an attorney's client cannot be excluded from a mixed DNA profile in which he or she can only be partially included. The attorney may decide to get a second opinion by a DNA expert to see if he or she agrees with the findings and to check if the test results support the conclusions. Because not every DNA profile is straightforward, there may be many interpretations. The DNA expert may request to review the lab's Standard Operating Procedures (SOP), as this information helps in understanding the basis for their conclusions. It may be a situation in which a DNA expert disagrees with the findings and can testify to this.

Scenario C: "Is my evidence probative?"
DNA Diagnostics Center (DDC) recently had a case in which a sexual assault occurred in an alley. A condom was collected from the scene and analyzed for DNA by a crime lab. Semen was found on one side of the condom, and only that side was swabbed for DNA. The DNA profile matched the suspect, and, at the time, he said that it was the condom he used with his girlfriend. In this case the evidence is not probative unless the victim's DNA is on the other side of the condom. The lab should have tested both sides! In many reports we find that there is not much stated about the source of the DNA or where on the evidence the DNA originated. Many questions come up as to whether the sample was consumed and if serology tests were performed. It is during case review that a DNA expert can piece all of information together for the attorney.

DNA experts at DDC have been able to assist attorneys in such scenarios. Based on the progress of the case, the attorney and our experts will work together to determine what forensic services are needed in their specific situation. As the following descriptions show, there is much more to forensic evaluation than just DNA testing.

DNA Report
In many cases, an attorney will approach DDC's expert with a DNA report from another lab. This 2- or 3-page report lists the items tested, which may or may not present the DNA profiles, states the results, and reports the conclusion. Quite often an attorney will send our experts a DNA report and ask if we agree with the report and if we thought any mistakes were made in the lab. Unfortunately, we can determine very little from a 2-page report. This means that a more complete evaluation of the case file and subsequent case review may be necessary to determine the validity of the results.

Case Review
To evaluate the DNA report provided by the attorney, a request for discovery material is presented. DDC can provide the attorney with a list of items needed for case review. This list, entitled "Request for Discovery," includes the case file and its contents such as the bench notes, worksheets, raw data (also known as electropherograms), allelic charts, statistical calculations, and the reports. Other items of importance include the lab's SOP, Quality Assurance Manual, electronic data, contamination records, accreditations, proficiency testing results, and the forensic analyst's CV.

Periodically an attorney will also request a letter or affidavit from the expert to include in their motion for discovery. The letter can outline what the expert will review, how long it will take, and how much it will cost. The case review will generally take 5 to 10 hours.

During the entire process of evidence evaluation, many questions may arise. In addition to analyzing DNA results, our forensic experts will think through the case from a forensic perspective. They will consider the implications of the serology tests and other scientific findings. Case review has also been helpful in establishing if DNA evidence is really probative. Forensic evaluation through case review may reveal information not yet illuminated in the process.

After case review, we offer consultation to the attorney, during which we provide him or her with our findings. It is during the consultation with the attorney that continuing education on DNA and serology can be given in whatever detail the attorney would like. Following this, the attorney may request a report of our findings.

DNA Testing
From time to time it comes up in court that a DNA sample needs to be consumed during testing. The attorney may opt to have their expert observe the testing process at the crime lab or to have the sample sent to their independent lab for testing and observation. Our experts at DDC have participated in both scenarios.

Some attorneys approach DDC first with a request for our DNA testing services. Other times, it is after review and consultation that the attorney may request DNA testing of the evidence. The methodology used nowadays produces DNA results that are reliable and hard to dispute. DNA is powerful if the test is done properly, but anyone who works in a DNA lab knows that mistakes can be made. This is why precautions are taken and policies are written to ensure good lab practices are followed. For instance, it is critical to run reference standards and evidence samples separately to make sure samples are not accidentally switched or contaminated. The use of positive and negative controls, throughout the DNA process, is essential to ensure that the method is working properly and that contamination does not occur.

With the information gleaned from DNA testing and case review, has reasonable doubt been established?

As technology and methodology evolve, so do our experts' knowledge and experience. With the expertise gained through our many different cases, we are able to pass on valuable information to you.