ABSTRACT
Forensic scientists are often asked to compare two items of evidence to determine whether they have (or might have) a common source. Testimony about such comparisons is called forensic identification evidence. This type of evidence frequently plays a crucial role in criminal trials by helping to link the defendant to the crime. This chapter focuses on expert testimony that purports to make a 'source attribution', that is, a determination that two physical items have (or might have) a common source. Forensic scientists distinguish two types of matches: those in which the items share class characteristics, features that place them in the same category or class; and those in which the items share individual characteristics, a unique combination of features. The standards promulgated by latent print and toolmark examiners, which require experts to express conclusions with absolute certainty, are excellent examples of the disconnect that can arise between standards and science.
