By Robert D. Blackledge, M.S.
Mr. Blackledge is senior chemist at the Naval Criminal Investigative Service Regional Forensic Laboratory in San Diego, California.
(Offenders are changing the nature of sexual assault investigations by wearing condoms.)
In an age filled with potentially fatal sexually transmitted diseases, more and more individuals practice safe sex. Even perpetrators of sex crimes have begun to wear condoms.1 It is not likely that a fear of disease prompts this behavior. Rather, just as a burglar dons gloves to avoid leaving fingerprints, sexual offenders now wear condoms to avoid depositing seminal fluids.
Forensic experts typically identify sexual assault offenders by examining seminal fluid residues for sperm, proteins, blood grouping factors, and DNA profile. When sexual assailants use condoms, however, assuming no leaks or spills, this valuable evidence gets trapped inside the condom, which investigators may never recover. The same can be said for any traces from the victim–including vaginal cells, blood, and saliva–that otherwise might have been transferred to the assailant’s penis.
Nevertheless, when assailants use condoms, they leave behind other valuable evidence.
Types Of Condom Trace Evidence
Manufacturers produce condoms using a variety of materials, both natural and synthetic. Each manufacturer has its own formula, which may vary even among its different brands. Some condoms are made from lamb membranes, and one manufacturer recently introduced a model made from polyurethane plastic. Still, latex rubber condoms have, by far, the largest share of the market, perhaps because they cost considerably less.
In addition to the basic materials they use to produce condoms, manufacturers also add other substances, known as exchangeable traces, which comprise particulates, lubricants, and spermicide.
Condom manufacturers add finely powdered particulates to prevent a rolled-up latex condom from sticking to itself. Particulates found in different brands include corn starch, potato starch, lycopodium (a powder found in plants), as well as amorphous silica, talc, or other minerals. In the laboratory, forensic scientists use several different techniques to characterize these particles and compare them with those obtained from other condom brands.
Sexual assailants prefer lubricated condoms, probably for the same reason that they use petroleum jelly, that is, to facilitate their crimes.2 Many condom brands contain a liquid lubricant, which may be classified as either “wet” or “dry.” Both types of condom lubricant have an oil-like consistency, but wet lubricants are water-based and/or water-soluble, while dry lubricants are not.
Although many different manufacturers use the same dry lubricant, their viscosity grades sometimes differ. The forensic laboratory can recover these silicone oils easily from items of evidence and possibly associate them with a condom manufacturer.
Wet lubricants may contain either polyethylene glycol or a gel made from a combination of ingredients similar to those found in vaginal lubricants. Despite similarities to other products on the market, forensic examination can associate specific formulations with particular condom brands.
Both wet and dry-lubricated condoms also may contain the spermicide nonoxynol-9. Its recovery and detection, along with lubricant ingredients and particulates, can help show condom use and indicate the specific brand.
The Value Of Condom Trace Evidence
Condom trace evidence can assist investigators in several ways. It can help prove corpus delicti, provide evidence of penetration, produce associative evidence, and link the acts of serial rapists.
In Proving Corpus Delicti Traces associated with condoms can help prove corpus delicti, the fact that a crime has occurred. This evidence can support the claims of either the victim or the accused. For example, the U.S. military can prosecute personnel diagnosed as HIV-positive for aggravated assault if they engage in unprotected sex, even if it is consensual. If service men accused of aggravated assault claim that they did in fact wear a condom but it broke or slipped off, condom trace evidence can support that claim.