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.