Imaging mass spectrometry of fingermarks on brass bullet casings using sample rotation

A rotation stage was developed to allow the surface of bullet casings to be imaged under ultra-high vacuum (UHV) conditions using time-of-flight secondary ion mass spectrometry (ToF-SIMS). Experiments were performed over a period of seven months to determine how fingermarks deposited on the surface of Webley MkII revolver rounds change over time. Stitching software written in Python was used to combine image strips that were collected by performing ToF-SIMS analysis along the length of the revolver rounds. The ToF-SIMS analysis was performed by analysing a thin strip along the length of the casings, before rotating them through a few degrees and analysing a new strip. This process was repeated until the entire casing had been imaged. The resulting secondary ion images of the fingermarks were compared to optical images obtained from the same and similar rounds that had been exposed to cyanoacrylate fumes and subsequently stained using Basic Yellow 40 (BY40) dye. ToF-SIMS images were shown to display evidence of ridge and sweat pore level detail on samples that displayed no evidence of fingermarks when developed with cyanoacrylate and BY40. The effects of the curvature of the round casings on the morphology of fingermarks were also assessed. ToF SIMS images were compared to marks that had been deposited onto flat paper surfaces using ink. The distortions caused by differences in surface curvature and the deposition methods were found to be within acceptable limits.

A comparative evaluation of the disulfur dinitride process for the visualisation of fingermarks on metal surfaces

The disulfur dinitride process for fingermark visualisation was first reported a decade ago, with promising results obtained for a range of materials including metals. However, the friction sensitive nature of the material and difficulty of synthesis made routine use difficult. Many of these issues have since been addressed, making equipment and chemicals available to build an understanding of how the effectiveness of disulfur dinitride compares to other fingermark visualisation processes currently used on metal surfaces. This enables more informed advice to be given on selection of processes for treatment of metal items, an area of operational interest that encompasses weapons used in violent crime and the increasing incidence in metal theft. This paper reports a comparative study into the effectiveness of disulfur dinitride, cyanoacrylate fuming, vacuum metal deposition, gun blueing and wet powder suspensions on brass, bronze, copper and stainless steel. Experiments were conducted with the surfaces exposed to a range of environments including long term ageing, water/detergent washing, acetone washing and high temperature exposure. The results indicate that disulfur dinitride is an effective process for fingermark visualisation on metal surfaces, including those exposed to adverse environments, and may offer potential improvements over existing processes for those surfaces. Further work, including pseudo-operational trials, is recommended.

Detection of Fingermarks-Applicability to Metallic Surfaces: A Literature Review

There are many different fingermark visualization techniques available, and the choice of methodology employed may be dependent on the surface type. This comprehensive review of the scientific literature evaluates the methodologies of fingermark enhancement methods that are applicable to metallic surfaces; optical, physical, chemical, and physicochemical methods are critically discussed. Methods that are currently used and those that have the potential to reduce the cost and time required to process evidence and increase the recovery rates are considered and are assessed against the Centre for Applied Science and Technology (CAST) and the International Fingerprint Research Group (IFRG) guidelines. The use of chemical imaging techniques in particular has increased the potential to recover fingermarks of sufficient quality for identification purposes. Presently, there appears to be a lack of detailed research pertaining to validation and thorough casework studies for fingermark enhancement techniques. Further studies incorporating these guidelines are recommended.

The Effect of Varying the Composition of Fingerprint Sweat Deposits on the Corrosion of Brass and Fingerprint Visibility

Corrosion of α-phase brass by sebaceous sweat fingerprint deposits produced identifiable impressions in a majority of samples (n = 40) 4 days after deposition. Combining sebaceous with eccrine sweat yielded a greater percentage of identifiable fingerprint deposits, although this increase was not statistically significant. Production of identifiable fingerprints from eccrine sweat deposits was dependent on the sampling time of year with deposits taken during summer months giving similar percentages of identifiable fingerprints to sebaceous deposits. A statistically significant positive correlation was found between elapsed days after deposition and identifiable eccrine (ρ = 0.787, p < 0.05), sebaceous (ρ = 0.724, p < 0.05), and eccrine/sebaceous mixture (ρ = 0.908, p < 0.01) fingerprints deposited during summer months. The summer increase in the percentage of identifiable eccrine sweat deposits was statistically significant compared to winter eccrine deposits (p < 0.0001). Observations were consistent with results obtained from artificial sebaceous and eccrine sweat.

An objective fingerprint quality-grading system

The grading of fingerprint quality by fingerprint examiners as currently practised is a subjective process. Therefore, an objective system was devised to remove the subjectivity. The devised grading system is quantitative and uses three separate, easily available, software packages to ultimately identify the portions of a fingerprint that correspond to low-, medium-, and high-quality definitive minutiae as defined on the Universal Latent Workstation of the US Federal Bureau of Investigation.

A comparison of fingerprint sweat corrosion of different alloys of brass

Fingerprint sweat from 40 donors was deposited onto samples of five α and α + β phase brasses, comprising five alloys with different copper and zinc concentrations, two of which also had the addition of small concentrations of lead. Visual grading of the visibility of the corrosion revealed that brasses with the least amount of zinc produced the most visible and fully formed fingerprints from the most donors. Consideration of previously reported mechanisms for the corrosion of brass suggests red copper (I) oxide as a likely corrosion product for low zinc brasses, and a consideration of the color, composition, and solubility of fingerprint sweat corrosion products suggests that copper (I) oxide produces good contrast and visibility with the brass substrate. Scanning electron microscope images of the corrosion of all five alloys confirmed the enhanced contrast between corroded and uncorroded areas for low zinc alloys.

Imaging fingerprint corrosion of fired brass shell casings

A newly developed method is presented for imaging fingerprint sweat corrosion of fired brass shell casings that reduces the degradation of the corroded fingerprint image. Degradation has been reduced by calculating a maximum angle of contact between the shell casing and a planar surface containing the imaging medium (graphite particles). Experiments have confirmed the predicted reduction in image degradation for contact angles less than the maximum. Details of the setup and operation of an instrument designed to improve fingerprint image quality are given and results shown for a 9 mm brass shell casing. Use of the instrument with other calibre ammunition is explained.

Latent fingermark visualisation using a scanning Kelvin probe

The current state of the art in fingermark visualisation on metallic surfaces by a scanning Kelvin probe (SKP) technique is described. Latent eccrine fingermarks deposited on a range of polished and roughened metallic surfaces can be effectively imaged. Results are presented which show that the SKP technique is able to visualise fingermarks obscured beneath optically opaque soot films and retrieve ridge detail in instances where fingermarks have been physically removed (e.g. by rubbing with a tissue) from a metal surface. SKP Volta potential mapping of small, severely non-planar metal objects such as fired brass cartridge cases is demonstrated.

Detection of visible and latent fingerprints using micro-X-ray fluorescence elemental imaging

Using micro-X-ray fluorescence (MXRF), a novel means of detecting fingerprints was examined in which the prints were imaged based on their elemental composition. MXRF is a nondestructive technique. Although this method requires a priori knowledge about the approximate location of a print, it offers a new and complementary means for detecting fingerprints that are also left pristine for further analysis (including potential DNA extraction) or archiving purposes. Sebaceous fingerprints and those made after perspiring were detected based on elements such as potassium and chlorine present in the print residue. Unique prints were also detected including those containing lotion, saliva, banana, or sunscreen. This proof-of-concept study demonstrates the potential for visualizing fingerprints by MXRF on surfaces that can be problematic using current methods.