Crime laboratory proficiency testing results, 1978-1991, II: Resolving questions of common origin.

A preceding article has examined the origins of crime laboratory proficiency testing and the performance of laboratories in the identification and classification of common types of physical evidence. Part II reviews laboratory proficiency in determining if two or more evidence samples shared a common source. Parts I and II together review the results of 175 separate tests issued to crime laboratories over the period 1978 to 1991. Laboratories perform best in determining the origin of finger and palm prints, metals, firearms (bullets and catridge cases), and footwear. Laboratories have moderate success in determining the source of bloodstains, questioned documents, toolmarks, and hair. A final category is of greater concern and includes those evidence categories where 10% or more of results disagree with manufacturers regarding the source of samples. This latter group includes paint, glass, fibers, and body fluid mixtures. The article concludes with a comparison of current findings with earlier LEAA study results, and a discussion of judicial and policy implications.