Types of Evidence
Applying DNA & Forensic Evidence to Your Criminal Defense Case
Curious about the types of evidence that are used in criminal trials, appeals, and post-convictions? The study and application of DNA and forensic evidence is a core practice here at RaquinMercer.
Steve Mercer’s litigation experience in private practice and as the chief attorney for the Forensics Division of the Maryland Office of the Public Defender has focused on DNA/forensic science. Now he has partnered with Isabelle Raquin to provide DNA/forensic science solutions for defense attorneys.
Contact RaquinMercer today for information on consulting with Steve and Isabelle about discovering problems with DNA/forensic science in your case and developing solutions as robust as your need.
The most common types of biological evidence include blood, saliva, skin cells, perspiration, and more. Typically, the dual aim of the testing is to indicate the type of biological evidence and provide sufficient samples of biological evidence to allow DNA profiling. DNA is touted as the “gold standard,” but not all DNA is the same. The relentless demand for DNA evidence in criminal prosecutions and the development of swifter, more sensitive testing methods create opportunities for error in source attribution and the identification of bodily fluids.
Weapons evidence consists of:
- Firearms: handguns, rifles, or shotguns
- Ammunition: spent casings, fired projectiles, bullet fragments, and unfired bullets
- Gunshot residue: also known as GSR
Like other methods developed to produce evidence for use in criminal prosecutions, the discipline relies heavily on an examiner’s subjective judgment that is formed using a methodology, which lacks foundational reliability.
Fingerprint evidence consists of comparisons between “10-prints” (fingerprints collected from a known person) and latent prints (only partial prints of one or more fingers collected from evidence associated with a crime). Similar to other pattern impression disciplines created by and for law enforcement, there are gaps in the methodology when applied to complex real-world conditions that can bias an examiner’s subjective judgment.
Drug evidence includes drugs and drug paraphernalia like pipes, spoons, or papers found at a scene or on a person or used in a transaction. The scientific community has demonstrated the validity of certain drug testing methods, such as gas chromatography/mass spectrometry (GC/MS) or thin-layer chromatography (TLC), when used in accordance with validated protocols. The existence of reliable protocols does not, however, mean the protocols were actually followed by a law enforcement laboratory in real-world conditions. Testing of residue and synthetics are particular areas of concern.
Trace evidence describes the category of evidence that includes small, possibly microscopic material. It covers a wide variety of evidence, but most typically involve hair and fibers. A microscopic examination for optical similarities between questioned hairs or fibers and known hairs or fibers is a methodology unique to law enforcement, and the process is highly vulnerable to examiner bias, error, and exaggerated statements about weight and uniqueness. Gas chromatography/mass spectrometry (GC/MS) has long been the accepted method for qualitative analysis of synthetic fibers, but the collection and analysis of trace evidence and the reporting of results can be susceptible to error due to contamination, transfer, and bias.
Electronic and printed data include documents and electronics, as well as video and audio recordings and other forms of surveillance. Digital evidence is highly vulnerable to errors because the objective of a forensic analysis of digital evidence is not a purely qualitative undertaking. The purpose is to obtain evidence that implies the actions of a person associated with the data. Examiners may not account for systemic error in data collection. This problem is compounded by tunnel vision and a failure to consider alternative explanations for the data.
Medical & Pathology Evidence
Medical and pathology evidence include cause and manner of death, nature and extent of injuries, and accidental or non-accidental causes of trauma. Because the cause and manner of death or injury are inherently opinions, subjective judgment is required to formulate these legally non-binding conclusions. Often the circumstances of a death or injury, in particular the history provided by a caregiver, inform the degree of certainty for a doctor’s judgment—rather than empirical data establishing the foundational validity of an underlying medical or scientific phenomenon.
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Creative Evidentiary Solutions for Your Legal Needs
At RaquinMercer, not only do we strive to provide excellent customer service, but we also want to ensure you understand all of your available legal options. We enjoy the fight inherent in criminal cases and love to challenge every aspect of our clients’ cases, every step of the way. We thrive on the complexity of cases involving forensic science; no case and no science is too difficult for us to comprehend or too hard to contest.
To learn more about our professional criminal defense attorneys serving Rockville, Potomac, DC, and other surrounding areas, contact us today!