When readers hear the term forensic evidence, they may assume that DNA analysis is involved. However, the term is much broader, encompassing the analysis of fingerprints, hair, bite marks and ballistics.
Yet not all analytical techniques are the same. One of the cornerstones of the scientific method is reproducibility, or the possibility of accurately replicating a reported test result. According to a committee report from the National Academy of Sciences, DNA evidence is the only form of forensic evidence that produces reliable and consistent evidence. Regarding ballistics and handwriting analysis, the report characterized them as based on untested science.
If other forms of forensic evidence do not hold up to the scientific method, readers may wonder why they appear so frequently in the prosecution of violent crimes, such as sexual assault or homicide. As a criminal defense attorney knows, DNA evidence may not have been collected in every case. For crimes where the prosecution is basing its case on non-DNA evidence, the court may allow other forms of forensic evidence to be submitted, perhaps with a jury instruction about its possible fallibility.
Yet entrusting a jury to properly weigh the credibility of non-DNA forensic evidence may be naïve. Certain evidence can make an emotional impact that overshadows any probative value it may offer. In the case of forensic evidence, television shows and movies have skewed the perception for many of us about the reliability of non-DNA evidence. That’s where the work of an experienced attorney can begin. An attorney can move to exclude overly prejudicial evidence, request a jury instruction specifically tailored to those concerns, and work to ensure that a criminal defendant receives a fair trial.
Source: Slate, “Forensic Science Isn’t Science,” Mark Joseph Stern, June 11, 1014