DNA Discovery for Defense Attorneys: The 5 Essentials your Expert will Need

If you’re a defense attorney with a new DNA case, you’ll want to request documents and files from the crime lab. Although I always suggest that attorneys seek an independent forensic DNA expert to assist (DNA evidence is complex and often confusing), you may wish to get a head start by requesting the 5 most essential items in advance. That way, your expert can get started more quickly once you retain them or get a court order to cover their fees.

1: Crime Lab Reports

Most likely, you’ve already received at least one report from the crime lab that alerted you that DNA evidence is an issue in your case. A crime lab report (sometimes called a Forensic Biology Report or Physical Evidence Examination Report) lists the items the lab received for testing, which items were tested and for what, and the results of the analyses. Typically, there are five steps in DNA testing: Serology (the identification of body fluids), DNA extraction, DNA quantitation, DNA profiling, and profile interpretation. In future posts, I’ll be revisiting each of these steps in detail. For now, be alerted that the lab may issue multiple reports for the same case. Be sure to request all reports pertaining to the case so you don’t miss one.

2: Analyst Bench Notes

Crime lab reports summarize the lab’s work but provide few details. The analyst’s bench notes provide critical information that can make or break a case. For example, a crime lab report might state “sperm were detected,” but provide no indication on the number of sperm (One? A few? Dozens? Such information could be helpful in determining if, when and how sexual contact took place). Similarly, the report might strongly include your client as a source of DNA on an item, but fail to note that DNA from only a handful of cells led to that conclusion. A DNA expert will read the bench notes carefully to pick up details that can have a significant impact on how you build your defense.

3: Digital DNA files

Digital DNA files are the raw data files that the crime lab generatsin the final stages of DNA testing. These files have “fsa” or “hid” extensions and often arrive on a thumb drive or CV. They can’t be opened and interpreted without specialized DNA software. Once generated, the crime lab will remove what they believe are profile artifacts and decide how many individuals they believe are present in the profile. Realize that these decisions are somewhat subjective and can significantly impact the DNA results reported by the lab (inclusions/exclusions of persons, including your client, as the source of the DNA). Your DNA expert may disagree with the lab’s interpretation, but they have no means to do so without examining the raw data files for themselves.

4. Probabilistic Genotyping Reports

Request any/all probabilistic genotyping reports. An ever-increasing number of labs have adopted probabilistic genotyping software to deconvolute mixtures, exclude persons as possible contributors, and provide statistical weights to inclusions. The most common software is STRmix. Ask for these reports so your expert can confirm that diagnostic thresholds were met and that the lab’s conclusions are scientifically sound.You can open and read the files for yourself, but if you don’t have STRmix training and expertise, you’ll have difficulty understanding them.

5. Police Reports

DNA experts usually want to review police reports so they can contextualize the DNA evidence. They need to know where each item of evidence was collected and how the lab’s findings fit into the opposing theories of the prosecution and the defense. The presence of sperm on a vaginal swab is nob-probative if the victim and suspect both agree to having sex (e.g. the victim claims it was non-consensual and the suspect claims it was consensual). Likewise, the presence of trace DNA on the neck of a victim may fall within the range of “background DNA” that’s likely to be on a woman’s neck at any given time and may have been deposited there long before the crime took place.

It’s best to provide your expert only with the police reports pertinent to the DNA findings, at least at first. Handing them a huge package of discovery to sort through wastes time and money. You might consider providing them with a synopsis of the case (a few paragraphs) to help them out. If they think they need more information, they can request to see the original police reports for more detail.

Your DNA expert will likely ask for additional discovery, including chain of custody documentation, CVs of the DNA analysts, proof of lab accreditation, the laboratory’s Standard Operating Procedures (SOPs) and more. Depending on the budget allotted for their work, and the details of the case, the expert may (or may not) decide to review them.

If you want to learn more: Dr. Ruth Ballard CV or contact me today

Ruth Ballard PhD, Forensic DNA Expert

Lending attorneys a helping hand since 1998.

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