cleaned with acetone prior to firing to remove the lacquer. Two lacquer-coated and two lacquer-stripped casings fired from each of three different guns were entered into the New York City Police Department’s IBIS and scores were generated; at the time, the number of 9mm Luger, circular firing pin exhibits (the base set for this comparison) in the New York system was estimated at 5,700 images. Generally, guns known to produce clear characteristic breech face marks performed consistently regardless of the presence of lacquer, which is to say that pairs of lacquer-coated exhibits from the same gun were returned in the top ranks as were pairs of lacquer-stripped exhibits; guns known to produce fainter breech face marks produced lower-ranked matches, yet still generally in the top 10. However, matching lacquer-coated to lacquer-stripped exhibits from the same gun proved more problematic, apparently failing to clear the coarse correlation and 20 percent threshold steps for guns with weaker propensity to generate breech face marks (score reported as 0 and rank as “none”; Hayes et al., 2004:Table 1).
The IBIS function for comparing bullet evidence plays a prominent role in a multi-part examination of criteria for identifying bullet matches, and in particular standards for the number of groups of consecutive matching striations that can be said to define a match (Miller and McLean, 1998; Miller, 2000, 2004; see also Miller, 2001).
The committee’s own experimentation, conducted by NIST under a separate contract with the National Institute of Justice, involved reanalysis of some of the De Kinder et al. (2004) cartridge casings as well as construction of a new 144-exhibit set of test-fired casings, varying ammunition brand and gun manufacturer. These casings were processed using both IBIS and three-dimensional metrology techniques, and were also run through IBIS waiving the coarse comparison and 20 percent threshold steps. We also performed limited IBIS experimentation using the New York CoBIS RBID and the independent IBIS database of the New York Police Department. We discuss the full details in Chapter 8; in brief summary, our own investigation corroborated the major findings of the predecessor studies described in this chapter.
The committee was charged to offer advice on the options of maintaining the current NIBIN program (limited to crime gun evidence) or enhancing it, and since NIBIN uses IBIS as its technical base, the evaluation of one requires evaluation of the other. Yet focusing too much on assessment of current IBIS is also somewhat unfair in light of the charge to our committee to evaluate the feasibility of a national RBID. As De Kinder et al. (2004:208) note, “currently, no technology has been perfected to deal spe-