A new Raman-based apparatus for proximal detection of energetic materials on people, was developed and tested for the first time. All the optical and optoelectronics components of the apparatus, as well as their optical matching, were carefully chosen and designed to respect international eye-safety regulations. In this way, the apparatus is suitable for civil applications on people in public areas such as airports and metro or railway stations. The acquisition software performs the data analysis in real-time to provide a fast response to the operator. Moreover, it allows for deployment of the apparatus either as a stand alone device or as part of a more sophisticated warning system architecture made up of several sensors. Using polyamide as substrate, the apparatus was able to detect surface densities of ammonium nitrate (AN), 2-methyl-1,3,5-trinitrobenzene (TNT), 3-nitrooxy-2,2-bis(nitrooxymethyl)propyl] nitrate (PETN) and urea nitrate (UN) in the range of 100–1000 μg/cm² at a distance of 6.4 m using each time a single laser pulse of 3 mJ/cm². The limit of detection calculated for AN is 289 μg/cm². AN and UN provided the highest percentages of true positives (>82% for surface densities of 100–400 μg/cm² and fingerprints) followed by TNT and PETN (17%–70% for surface densities of 400–1000 μg/cm² and fingerprints).

In this work, we present a compact LIBS sensor developed for characterization of samples on a crime scene following requirements of law enforcement agencies involved in the project. The sensor operates both in a tabletop mode, for aside measurements of swabbed materials or taken fragments, and in handheld mode where the sensor head is pointed directly on targets at the scene. The sensor head is connected via an umbilical to an instrument box that could be battery-powered and contains also a color camera for sample visualization, illumination LEDs, and pointing system for placing the target in focus. Here we describe the sensor’s architecture and functionalities, the optimization of the acquisition parameters, and the results of some LIBS measurements. On nano-plotted traces at silica wafer and in optimized conditions, for most of the elements the detection limits, in term of the absolute element masses, were found to be below 10 picograms. We also show results obtained on some representative materials, like fingerprints, swabbed soil and gunshot residue, varnishes on metal, and coated plastics. The last, solid samples were used to evaluate the depth profiling capabilities of the instrument, where the recognition of all four car paint layers was achieved.

Stand-off detection of latent traces avoids the scene alteration that might occur during close inspection by handheld forensic lights. Here, we describe a novel sensor, named Crime Light Imaging (CLI), designed to perform high-resolution photography of targets at a distance of 2–10 m and to visualize some common latent traces. CLI is based on four high-power illumination LEDs and one color CMOS camera with a motorized objective plus frontal filters; the LEDs and camera could be synchronized to obtain short-exposure images weakly dependent on the ambient light. The sensor is integrated into a motorized platform, providing the target scanning and necessary information for 3D scene reconstruction. The whole system is portable and equipped with a user-friendly interface. The preliminary tests of CLI on fingerprints at distance of 7 m showed an excellent image resolution and drastic contrast enhancement under green LED light. At the same distance, a small (1 µL) blood droplet on black tissue was captured by CLI under NIR LED, while a trace from 15 µL semen on white cotton became visible under UV LED illumination. These results represent the first demonstration of true stand-off photography of latent traces, thus opening the way for a completely new approach in crime scene forensic examination.

In this work we report the results of analysis of the acoustic signal generated by the interaction of a nanosecond laser pulse (30 mJ, 1064 nm) with various residues placed on a silica wafer. The signal was captured by a unidirectional microphone placed 30 mm from the laser-generated plasma. The examined sample classes, other than the clean wafer, included particles from soils and rocks, carbonates, nitro precursors, ash, coal, smeared diesel, and particles of explosives. We tested three types of explosives, namely PETN, RDX, and HMX, having different origins. For the explosives, the acoustic signal showed a faster rise, larger amplitude, different width, and attenuation compared with the other sample classes. By subtracting the acoustic signal from the wafer at the same position, obtained after four cleaning laser pulses, the contribution of echoes was eliminated and true differences between the residue and substrate became evident. Through four different features in the subtracted signal, it was possible to classify explosives without the presence of false positives; the estimated limit of detection was 15 ng, 9.6 ng, and 18 ng for PETN, RDX, and HMX, respectively, where the mass was extrapolated from nano-printed samples and LIBS spectra acquired simultaneously. Furthermore, HMX was distinguished from the other two explosives in 90% of the cases; diesel and coal were also recognized. We also found that explosives deposited through wet transfer behaved as inert substances for the tested masses up to 30 ng.

The visualisation of bodily fluid stains in crime scene evidence is often challenging due to the characteristics of the fluid, the substrate on which they are deposited, or the presence of look-alike substances that may confound the investigators. Hyperspectral imaging (HSI) combines conventional imaging with spectral analysis, enabling the simultaneous visualisation and spectral characterisation of stains. In this study, stains of blood, semen, oral fluid, and sweat, together with seven non-bodily fluid stains and five blood-semen mixed stains, were deposited on nine substrates varying in colour and porosity. All stains were analysed using two hyperspectral cameras operating in the visible-near-infrared and shortwave-infrared ranges. The study aimed to evaluate the discrimination potential of the fused data from both cameras using orthogonal partial least squares-discriminant analysis (OPLS-DA). Both cameras proved useful for the analysis of bodily fluid stains, each offering distinct advantages: The SPECIM iQ was more user-friendly, while the HERA SWIR-2 data provides the chemical fingerprint needed to confirm the nature of the stain, due to the specific vibrational overtones in the shortwave-infrared spectral range. Results demonstrated the visualisation and identification of all bodily and non-bodily fluid stains, as well as their discrimination, irrespective of the substrate. The synergistic value of the visible-near-infrared and shortwave-infrared data fusion is clearly demonstrated, particularly in the analysis of the complex blood-semen mixed stains. These findings highlight the significant potential of combining HSI with chemometric analysis for the detection, visualisation, and classification of bodily fluid stains in forensic investigations.