Joanne B. Sgueglia, Ann C. Juston and Jack Ballantyne
Suffolk County Crime Laboratory, Hauppauge, New York

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Three sexual assault cases were analyzed using the following STR multiplexes: British Home Office Quadruplex (vWA, TH01, F13A and FES/FPS), AmpFISTR Blue (D1S1358, vWA and FGA) and AmpFISTR Yellow I (Amelogenin, TH01, TPOX and CSF1PO) which encompass a total of 8 loci and sex determination. The casework examples were specifically chosen to represent various sample types (blood, semen and saliva), differing DNA quantity and quality, the presence of amplification inhibitors, bacterial contamination and mixtures. One rape case involved saliva found on a bra in which no semen evidence was detected. Another case required processing an entire sanitary napkin in order to obtain sufficient human DNA amidst a large amount of bacterial DNA. The last case involved four individuals (victim, two suspects and a boyfriend) and numerous semen stains which yielded some interesting data for mixture interpretation. These cases had previously been analyzed using RFLP and, in one instance, PCR (HLA DQa ) methodology. A comparative analysis demonstrated good correlation between original data and the STR data and these results will be presented in some detail with emphasis on some of the more provocative findings.

This study demonstrates the general usefulness of multiplex STR markers in routine casework but exemplifies the need for caution in mixture interpretation.