The National Research Council recently released the third edition of the Reference Manual on Scientific Evidence, a manual developed to guide judges when they encounter scientific evidence at trials.
The manual contains chapters on the admissibility of expert testimony as well as on particular topics of forensic science, including DNA evidence, toxicology, neuroscience, mental health evidence, statistics, and forensic identification evidence (fingerprints, firearm identifications, bite marks and microscopic hair evidence).
A free PDF version of the manual can be downloaded here, or it can be read online or a hard copy may be purchased. There already has been some discussion of the manual online, including by the blog Grits for Breakfast, which discusses the manual here in a post about hair analysis and here in a post about firearm identification evidence.
In addition to providing guidance to judges on how to address scientific evidence, the manual suggests best practices for defense attorneys. Defense attorneys can use portions of this manual to support their arguments at trial as well as to assess their approach to defending cases in light of new information about forensic evidence. Professor Margaret A. Berger’s chapter, The Admissibility of Expert Testimony, makes recommendations about defense challenges to particular techniques, use of defense experts, cross examination, and jury instructions.
Berger raises concerns about testimony on subjective identification techniques, which are techniques that involve the visual comparison of one item of evidence to another (for example, fingerprint comparison, firearm and toolmark comparison, bite mark analysis, etc.). She recommends objecting to testimony that is not supported by scientific studies. For example, defense counsel should object to testimony about “zero error rates” which have not been proven scientifically. Additionally, a conclusion that there is a “match” between items of evidence should be objected to or clarified. Finally, attorneys should try to limit testimony that an expert can “individualize” an item to its particular source using a comparison technique. p. 29.
Berger recommends that defense attorneys use scientific studies to explain to the jury what forensic conclusions are permissible. She recognizes that defense counsel may need to call their own experts experts or request jury instructions in order to appropriately limit testimony that exceeds the bounds of science. p. 29.
This chapter, as well as others on particular fields of forensic science, are well worth a look.