title: Optimization of a statistical algorithm for objective comparison of toolmarks.
abstract: Due to historical legal challenges, there is a driving force for the development of objective methods of forensic toolmark identification. This study utilizes an algorithm to separate matching and nonmatching shear cut toolmarks created using fifty sequentially manufactured pliers. Unlike previously analyzed striated screwdriver marks, shear cut marks contain discontinuous groups of striations, posing a more difficult test of algorithm applicability. The algorithm compares correlation between optical 3D toolmark topography data, producing a Wilcoxon rank sum test statistic. Relative magnitude of this metric separates the matching and nonmatching toolmarks. Results show a high degree of statistical separation between matching and nonmatching distributions. Further separation is achieved with optimized input parameters and implementation of a "leash" preventing a previous source of outliers--however complete statistical separation was not achieved. This paper represents further development of objective methods of toolmark identification and further validation of the assumption that toolmarks are identifiably unique.
authors.affiliation: Ames Laboratory, Iowa State University, 2220 Hoover, Ames, IA, 50011.
authors.forename: Ryan
authors.initials: R
authors.lastname: Spotts
authors.forename: L Scott
authors.initials: LS
authors.lastname: Chumbley
authors.forename: Laura
authors.initials: L
authors.lastname: Ekstrand
authors.forename: Song
authors.initials: S
authors.lastname: Zhang
authors.forename: James
authors.initials: J
authors.lastname: Kreiser
keywords: algorithm; forensic science; pliers; quasi-striated; shear cutter; statistical comparison; striae; toolmark