Finding evidence at drug-facilitated crime and drug-facilitated sexual assault scenes: determination of two benzodiazepine residues in beverages

In cases of drug-facilitated crime (DFC) and drug-facilitated sexual assault (DFSA), beverages often contain tasteless, colorless, and odorless substances that dissolve easily in liquids and incapacitate victims. Most of these cases involve benzodiazepines such as diazepam (DIA) and flunitrazepam (FLU) because of their short duration of action and easy availability. In this respect, it is necessary to detect the presence or absence of these drugs in crime scene investigations, the evaluation of witness statements, and the investigation of traffic safety incidents. The development of new methods to assess the presence of these drugs in beverage residues or contaminated materials, which are commonly used in DFC/DFSA cases, is also crucial for proving complicity. This study aims to develop a rapid, sensitive, and reliable high-performance thin-layer chromatography (HPTLC) method to detect DIA and FLU in residual beverage samples. The method was validated with selectivity, linearity, limit of detection (LOD), limit of quantification (LOQ), precision, and accuracy. The linearity ranged between 6 and 40 ng/zone for both drug substances. The mean recovery values for DIA and FLU were 111.2% and 104.8%, respectively, with a relative standard deviation (%RSD) value ≤ 6. The validated method was successfully applied to residual beverage samples simulating DFC/DFSA cases to increase the validity of the study and to understand whether it can be applied to real residues. The amounts of DIA and FLU obtained from simulated samples were detected in the range of 8.4‒17.4 ng/zone. Results from simulated crime scenes demonstrate the suitability of the method for the examination of evidence recovered from suspected crime scenes and the possibility of identifying and analyzing evidence contaminated with trace amounts of these two active substances. This simple HPTLC technique offers a reliable tool for the rapid detection of these sedative-hypnotic drugs in real-world forensic cases. It can also provide valuable information for routine analysis and serve the interests of justice by validating the findings.