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Automated Processing of Sexual Assault Cases Using Selective Degradation

NCJ Number
Date Published
April 2012
75 pages
This research developed an optimized, validated process for obtaining single-source male DNA profiles from mixed stains, greatly improving the ability of law enforcement agencies to process and prosecute sexual assault cases.
The current standard differential extraction method leaves some amount of the female epithelial cell DNA in the sperm fraction of the sample, which may partially or completely mask the sperm DNA profile. This may prevent conviction or even detection of the perpetrator. The proposed process eliminates sperm fraction DNA profile mixtures from almost all sexual assault evidence that contains sperm cells. It often permits crime laboratories to obtain single-source male DNA profiles even in circumstances in which the standard method of differential extraction does not produce a sperm fraction male profile. As a result of this research, some cases in which a sexual assault suspect could not previously have been identified from a mixed DNA sample from the victim, forensic analysts will now be able to obtain a full DNA profile of the perpetrator. This procedure saves time for DNA analysts in performing differential extraction and also eliminates the time drain and uncertainty caused by mixed DNA profiles. In addition, it is possible to automate the differential extraction process. The current research used a nuclease to digest the remaining epithelial DNA in the sperm fraction of mock sexual assault samples. The research obtained clean single-source mal DNA profiles from mixed stains under a variety of sample conditions. The research also optimized this procedure, including reagent concentrations and volumes, followed by validation of the procedure for sensitivity, reproducibility, and precision. The results of this selective degradation approach were compared with the results obtained with the current standard method of differential extraction. The selective degradation methodology was determined to be compatible with the DNA purification methods currently used in public laboratories. 5 tables, 25 figures, 17 references, and a listing of publications and presentations of the research findings

Date Published: April 1, 2012