Serological Evidence in Sexual Assault Investigations

Miscellaneous Samples

The officer should make sure that the clothing worn by the victim during the sexual assault is collected. The victim should always disrobe over examination paper. The victim’s panties, pantyhose, jeans, shirt, shoes, socks, dress, or nightgown should be separated and individually packaged as appropriate. Any physical evidence from the crime scene that may bear suspected semen stains, such as bed sheets, towels, wash cloths, paper towels, toilet paper or tissue paper, should also be collected. The examination paper should also be submitted for analysis in the event that hair or fiber mixtures from the assault fell from the victim while disrobing.

The collected items should be clearly described for the laboratory, including whether the items came in contact with the victim and/or suspect before, during, and/or after the assault. Stained areas believed to exhibit evidence of the assault should be described or highlighted. For example, only a small area on a bed sheet may be relevant to the investigation. Therefore, forensic examination of the entire bed sheet for semen may not only be unnecessary and wasteful of forensic services but may also dilute the effectiveness of the examination.

Preservation And Packaging

Bacteria begin to degrade biological fluids immediately after deposition. They especially thrive on the rich nutrients present in semen. If unchecked,contaminant bacteria can completely destroy DNA and other genetic markers of value. To counteract this phenomenon in all of the above instances in which moist body fluids are collected, it is imperative that the samples be completely dried. After drying, the specimen(s) should be placed into breathable paper bags or envelopes and frozen or refrigerated until submitted to the laboratory for analysis.

All collected items of evidence should be properly cataloged with preserved chain-of-custody records for court presentation purposes. All items should be dated and initialed by the collector. In cases where samples were taken by health professionals, they should identify, date and initial the items and hand the evidence to the investigating officer. Whenever possible, collection of known blood, urine and saliva samples should be performed under the supervision of the investigating police officer.


Each sexual assault occurs under circumstances unique to the victim, the crime scene, and the suspect. If extensive information is provided to the examiner in the crime laboratory, the examiner can conduct a more thorough and complete scientific analysis. Probative value and relevance to the investigation are the watch words in collecting and preserving the evidence of a sexual assault. If collected materials are stored in plastic bags under room temperature for any extent of time, the biodegrading action of contaminant bacteria may jeopardize conclusive test results. Sexual assault evidence kits with all of the above-mentioned materials are commercially available and stocked by hospitals and rape crisis centers.

Proper collection, identification, packaging and storing of evidence in sexual assault investigations will greatly improve the chances for a successful prosecution of the perpetrator, as long as the investigating officer follows up with good communication and contact with the laboratory examiner in all stages of the case. The evidence sent to the forensic laboratory should be accompanied by a transmittal letter that completely describes the facts of the crime, the inventory of the evidence seized, and the scientific examinations requested. It is suggested that the report of the initial examining physician be included along with the evidence.

Criminal investigators and prosecutors must familiarize themselves with proper procedures concerning the collection, identification, and packaging of serological evidence, as well as to establish effective communication with the examiner. By doing this, and by understanding the practical capabilities and limitations of modern forensic serology, the interests of justice can be best served with a successful prosecution of the perpetrator in a sexual assault.