Thermal development of latent fingermarks on porous surfaces—Further observations and refinements

Abstract

In a further study of the thermal development of fingermarks on paper and similar surfaces, it is demonstrated that direct contact heating of the substrate using coated or ceramic surfaces at temperatures in excess of 230 C produces results superior to those obtained using hot air.Fingermarks can also be developed in this way on other cellulose-based substrates such as wood and cotton fabric, though ridge detail is difficult to obtain in the latter case.Fluorescence spectroscopy indicates that the phenomena observed during the thermal development of fingermarks can be reproduced simply by heating untreated white copy paper or filter paper, or these papers treated with solutions of sodium chloride or alanine. There is no evidence to suggest that the observed fluorescence of fingermarks heated on paper is due to a reaction of fingermark constituents on or with the paper. Instead, we maintain that the ridge contrast observed first as fluorescence, and later as brown charring, is simply an acceleration of the thermal degradation of the paper. Thermal degradation of cellulose, a major constituent of paper and wood, is known to give rise to a fluorescent product if sufficient oxygen is available.[1-5] However, the absence of atmospheric oxygen has only a slight effect on the thermal development of fingermarks, indicating that there is sufficient oxygen already present in paper to allow the formation of the fluorescent and charred products. In a depletion study comparing thermal development of fingermarks on paper with development using ninhydrin, the thermal technique was found to be as sensitive as ninhydrin for six out of seven donors. When thermal development was used in sequence with ninhydrin and DFO, it was found that only fingermarks that had been developed to the fluorescent stage (a few seconds of heating) could subsequently be developed with the other reagents. In the reverse sequence, no useful further development was noted for fingermarks that were treated thermally after having been developed with ninhydrin or DFO. Aged fingermarks, including 3 marks from one-year-old university examination papers were successfully developed using the thermal technique.

Microwave Selective Thermal Development of Latent Fingerprints on Porous Surfaces: Potentialities of the Method and Preliminary Experimental Results

“…As well evident from the comparison between Figs a and b, the use of microwave heating for the thermal development of latent eccrine‐rich fingerprints on porous paper‐based substrate (Fig. a) led to results comparable to those of eccrine‐rich residues developed by the already optimized direct contact heating method (Fig. b), in terms of a good contrast with the background substrate and in terms of ridge details and possibility to easily identify basic minutiae of the developed pattern.…”

“…However, the possible introduction of microwave selective heating into the sequential processing of latent fingerprints on porous surfaces is currently under testing, together with split depletion experiments, aiming to comparatively investigate the sensitivity of the here‐proposed microwave technique with the direct contact heating method (as optimized by Song et al. ) and with more conventional chemical ones, according to the experimental methodology recently proposed by Sears et al. to establish minimum standards to this innovative technique and bring some consistency to the process.…”

“…For this purpose, Song et al. recently focused their research efforts in the investigation of thermal development of latent fingerprints on porous surfaces by direct contact heating methods, using different heating surfaces. The best results were obtained with a commercial hair straightener device, with poor thermally conductive ceramic‐coated surfaces.…”

Portable hyperspectral imager with continuous wave green laser for identification and detection of untreated latent fingerprints on walls

“…When the wavelength of the excitation light is fixed so as to allow light absorption, the fluorescence wavelengths are in general longer than the excitation wavelength because of relaxation processes peculiar to the medium. Changes in fluorescence spectra due to the constituents of fingerprints/palm prints are thus attributed to their degeneration due to photochemical and thermal effects [4,[6][7][8][9][10][11].…”

Study of UV imaging technology for noninvasive detection of latent fingerprints

“…The noninvasive detection of latent fingerprints mainly use o ptical methods, for example, spectroscopic imaging methods [1,2,3], which can detect the most sweat latent fingerprint on common substrates using spectroscopic image techniques; intrinsic fluoresce detection technique, which can realize the noninvasive detection of latent fingerprint and improve the detection rate in lower temperature [4,5,6] using the principle that the intrinsic fluoresce luminous efficiency and intensity are increased with the temperature decreased; various optical photography detection techniques [7,8,9], and thermal development of latent fingerprints on porous surfaces [10,11,12]. * UV imaging technology is a noninvasive detection method of latent fingerprints , which use the UV light as light source, according to the special absorption、reflection、scattering and fluorescence characterization of the various residues in fingerprints (fatty acid ester, protein, and carbosylic acid salts etc) and evidence substrate material to the UV ligh t, to weaken or eliminate the background disturbance to increase the brightness contrast of fingerprints with the background, and use a imaging system to capture the digital image of fingerprint, realize the noninvasive detection and appearance of latent fingerprint on various substrates.…”