RESUMO
Visualization of latent fingerprints on metallic surfaces by the method of applying electrostatic charging and adsorption is considered as a promising chemical-free method, which has the merit of nondestruction, and is considered to be effective for some difficult situations such as aged fingerprint deposits or those exposed to environmental extremes. In fact, a portable electrostatic generator can be easily accessible in a local forensic technology laboratory, which is already widely used in the visualization of footwear impressions. In this study, a modified version of this electrostatic apparatus is proposed for latent fingerprint development and has shown great potential in visualizing fingerprints on metallic surfaces such as cartridge cases. Results indicate that this experimental arrangement can successfully develop aged latent fingerprints on metal surfaces, and we demonstrate its effectiveness compared with existing conventional fingerprint recovery methods.
RESUMO
Nondestructive techniques for gathering evidence are important in the field of forensics. Due to the geometry of the substrates, nondestructive visualization of fingermarks on curved surfaces remains challenging. A novel contactless technique was developed for visualizing and recording fingermark patterns on nonporous curved surfaces of circular cross section. The technique utilizes a plane mirror to transmit rays from a light source to illuminate the area of interest for fingermark visualization. The fingermark acquisition system consists of a digital single-lens reflex (SLR) camera, a plane mirror, and a white light source. Mathematical equations are used to calculate the mirror size. Experiments were performed on various curved surfaces to determine the feasibility and effectiveness of the technique. Spectral Image Validation and Verification (SIVV) was used to analyze the captured images. The results of this study indicate that the technique described here is able to reveal fingermark patterns on curved surfaces of circular cross section.
RESUMO
A method has been developed for the visualization of latent fingerprints on fabrics, which is based upon cyanoacrylate (superglue) fuming followed by imaging using an infrared microscope. Results show that imaging on smooth, shiny fabrics such as polyester, silk, nylon, and acetate of different colors and patterns can give an improvement over existing enhancement methods. Results for cotton and polycotton were less successful and it is thought this may be due a combination of the presence of the carbonyl functional group in these fabrics as well as their absorbency to fingerprint sweat. The carbonyl peak (1700 cm(-1) ) provided the optimum spectroscopic feature to map and image a fingerprint. Comparisons between infrared mapping at a specific frequency range and principal component analysis showed that improved imaging was obtained with principal component analysis.
RESUMO
Latent fingerprint deposits on thermal paper sourced from the U.S., China, the U.K., and Australia have been visualized by heating. U.S. and Chinese sourced paper produced two distinct types of fingerprint development. In one type (type 1), the paper dye colors where the deposit is present (as previously reported) and in the other type (type 2) the 'inverse' of this gives paper coloring only in areas not coincident with the deposit. Both development types gave identifiable fingerprints, the majority fading within 24 h of heating. Fingerprint development from U.K. and Australian sourced paper was exclusively type 1 and resistant to fading. Temperatures for fingerprint visualization were higher for U.S. paper (64-71°C) and Chinese paper (75-95°C) than for U.K. and Australian sourced paper (43-50°C). Particularly for Chinese sourced paper, these temperatures were within a few degrees of the normal paper color temperature. A mechanism for type 2 fingerprint development is proposed.
RESUMO
Latent fingerprint deposits on thermal paper have been visualized noninvasively at visible wavelengths when illuminated with a UV-A light source (peak 365 nm). A higher intensity UV source (250 W/m(2) at 0.38 m) gave superior fingerprint visibility when compared with a 60 W/m(2) (at 0.4 m) source. Removing the visible (blue) component of the light source emission did not adversely affect the visibility of the fingerprint. Sample fingerprints from 100 donors, when examined 24 h after deposition, produced identifiable fingerprints from nearly 34% of fingerprint deposits. A mechanism for the observed visibility is proposed based on low emission of visible wavelengths from areas of thermal paper coincident with the fingerprint deposit, when illuminated with UV. This is likely due to a weak color change in the thermal paper dye arising from protonated amino acid components of the sweat. This effect was not observed on nonthermal paper.
RESUMO
A calibration test is described for monitoring the operation of equipment used to develop latent fingerprints on thermal paper by the application of either controlled or uncontrolled heat. A working solution of a water/glycerol emulsion and butylene glycol is applied to thermal paper by means of either a vinyl stamp and pad, or a marker pen. Varying the amount of butylene glycol enables the thermal paper to change color at different temperatures between approximately 40 and 60°C, which is below the normal color change temperature of the paper. The described test may be used to verify the correct operation, at different temperatures, of a controlled heat source during and after fingerprint development (such as the Hot Print System) or to monitor the paper temperature with an uncontrolled heat source (such as a warm air blower), thereby avoiding unintentional coloring of the entire paper surface.