The Role of Hair Analysis in the Investigation of Drug-Facilitated Rapes

Marco Vincenti, Department of Chemistry, University of Torino, Torino, Italy
                              Director of the Regional Antidoping and Toxicology Center “A. Bertinaria”, Torino, Italy

“Drug-facilitated crimes” (DFC) are perpetrated when the victims are subjected to non-consensual acts while they are impaired by the effects of one or more drugs, frequently administered surreptitiously. They include rapes and sexual assaults, which represent most part of DFC. This impairment disables the victim to offer resistance to the rape, both physically and psychologically, due to the multiple pharmacological effects of most psychoactive substances. Moreover, several drugs produces anterograde amnesia, that makes the victim’s testimony extremely feeble during the subsequent investigation and trial.

Whenever the victim does not report the crime to the police within few hours, either because she/he is intimidated or incapacitated, the drug is progressively metabolized and excreted, leaving faint trace in the body fluids, until it becomes undetectable after 1-4 days, depending on the chemical properties of the drug and its administered dose. Under such circumstances, a delayed hair analysis becomes a crucial means to assess the single drug intake and its chronological occurrence. An extremely low fraction of almost any drug gets incorporated into the keratin hair structure by means of various mechanisms involving either capillary blood, sebum, or sweat. This fraction remains permanently fixed within the inner hair structure, from which it can be recovered and detected even months later.

Generally, head hair is collected from the vertex posterior about 6 weeks after the offense. The hair should be cut as close as possible to the scalp, in a pencil-sized thickness, from which 2-3 aliquots can be partitioned. One aliquot is used for the screening or for both screening and confirmation. The common analytical procedure encompasses the following steps: (1) external decontamination; (2) segmentation; (3) pulverization; (4) extraction; (5) clean-up or fractionation; (6) detection and quantification. All the analytical steps should be optimized taking into account the specific objectives/questions involved in the casework. The final detection phase is carried out with either targeted or untargeted procedures, depending on the clues collected during the investigative work.

A well-focused hair segmentation is crucial for the subsequent interpretation of the analytical results. Supposing an average 1-cm hair growth, the hair lock is generally cut into 0.5-1.0 cm segments. In order to prove single exposure to the alleged “rape drug” unambiguously, i.e. to exclude habitual consumption of it, the following criteria should be met: (a) the initial 1-2 segments correspondingly closest to the scalp should not contain the drug; (b) the subsequent 1-2 segments chronologically corresponding to the time-frame of the rape should contain the drug; (c) the detected concentrations of the drug should be compatible with a single intake; (d) the farthest hair segments should again be free from the drug. Several other interpretation issues will be presented in the lecture, including the chemical properties of the drug and the potential sources of bias.