John W. Bond

Visualization of Latent Fingerprint Corrosion of Metallic Surfaces

Abstract:  Chemical reactions between latent fingerprints and a variety of metal surfaces are investigated by heating the metal up to temperatures of ∼600°C after deposition of the fingerprint. Ionic salts present in the fingerprint residue corrode the metal surface to produce an image of the fingerprint that is both durable and resistant to cleaning of the metal. The degree of fingerprint enhancement appears independent of the elapsed time between deposition and heating but is very dependent on both the composition of the metal and the level of salt secretion by the fingerprint donor. Results are presented that show practical applications for the enhancement to fingerprints deposited in arson crime scenes, contaminated by spray painting, or deposited on brass cartridge cases prior to discharge. The corrosion of the metal surface is further exploited by the demonstration of a novel technique for fingerprint enhancement based on the electrostatic charging of the metal and then the preferential adherence of a metallic powder to the corroded part of the metal surface.

Value of DNA Evidence in Detecting Crime

ABSTRACT: DNA material is now collected routinely from crime scenes for a wide range of offences and the timely processing of the DNA is seen as key to its success in investigating and detecting crime. An analysis of DNA material recovered from the volume crime offences of residential burglary, commercial burglary, and theft of motor vehicle in Northamptonshire, U.K., in 2004 has enabled the DNA to be categorized into seven sources. Further analysis using a logistical regression has revealed a number of predictors, other than timeliness, that greatly influence whether the DNA material recovered from a crime scene enables the crime to be detected. The results indicate that a number of these predictors are of statistical significance and may be just as relevant in determining whether DNA successfully detects the crime as the timeliness of the processing of the DNA material. The most significant predictor was found to be investigating officer accreditation with location, quantity, and type of DNA material at the crime scene also being relevant. Accreditation of the Crime Scene Examiner recovering the DNA material was found not to be significant. Consideration is given to where further emphasis is needed by the U.K. police service to maximize the opportunities to detect volume crime with DNA.

The Value of DNA Material Recovered from Crime Scenes

Abstract:  DNA material is now collected routinely from crime scenes for a wide range of offenses and its timely processing is acknowledged as a key element to its success in solving crime. An analysis of the processing of approximately 1500 samples of DNA material recovered from the property crime offenses of residential burglary, commercial burglary, and theft of motor vehicle in Northamptonshire, U.K. during 2006 identified saliva and cigarette ends as the main sources of DNA recovered (approximately 63% of samples) with blood, cellular DNA, and chewing gum accounting for the remainder. The conversion of these DNA samples into DNA profiles and then into matches with offender profiles held on the U.K. National DNA database is considered in terms of the ease with which Crime Scene Examiners can recover DNA rich samples of different sources, the location of the DNA at the crime scene, and its mobility. A logistical regression of the DNA material recovered has revealed a number of predictors, other than timeliness, that greatly influence its conversion into a DNA profile. The most significant predictor was found to be Crime Scene Examiner accreditation with offense type and DNA sample condition also being relevant. A similar logistical regression of DNA samples profiled that produced a match with an offender on the U.K. National DNA database showed no significance with any of the predictors considered.

Linking different types of crime using geographical and temporal proximity

In the absence of forensic evidence (such as DNA or fingerprints), offender behavior can be used to identify crimes that have been committed by the same person (referred to as behavioral case linkage). The current study presents the first empirical test of whether it is possible to link different types of crime using simple aspects of offender behavior. The discrimination accuracy of the kilometer distance between offense locations (the intercrime distance) and the number of days between offenses (temporal proximity) was examined across a range of crimes, including violent, sexual, and property-related offenses. Both the intercrime distance and temporal proximity were able to achieve statistically significant levels of discrimination accuracy that were comparable across and within crime types and categories. The theoretical and practical implications of these findings are discussed and recommendations made for future research.

The Thermodynamics of Latent Fingerprint Corrosion of Metal Elements and Alloys

Abstract:  Redox reactions taking place between the surface of a metal and fingerprint residue have been expressed thermodynamically in terms of both the Nernst equation for reduction potential and the complexation constant for the formation of complex metal halide ions in aqueous solution. These expressions are used to explain experimental results for the corrosion of 10 different metal elements by fingerprint residue in air at room temperature. Corrosion of noble metals, such as silver and gold, supports the proposition that the degree of metal corrosion is enhanced by the presence of chloride ions in eccrine sweat. Extending the experiments to include 10 metal alloys enabled the construction of a fingerprint corrosion series for 20 different metals. Fingerprint corrosion on metals alloyed with > ∼40% copper was found to display third level fingerprint detail. A comparison of both conventional ink on paper and digital (Livescan) fingerprinting techniques with fingerprints deposited on 9 Karat gold alloy has shown that gold alloy depositions are least susceptible to third level detail obliteration by poor fingerprint capturing techniques.

Use of Data Mining Techniques to Model Crime Scene Investigator Performance

This paper examines how data mining techniques can assist the monitoring of Crime Scene Investigator performance. The findings show that Investigators can be placed in one of four groups according to their ability to recover DNA and fingerprints from crime scenes. They also show that their ability to predict which crime scenes will yield the best opportunity of recovering forensic samples has no correlation to their actual ability to recover those samples.

Determining how journeys-to-crime vary: Measuring inter- and intra-offender crime trip distributions

Journey to crime studies have attempted to illuminate aspects of offender decision making that has implications for theory and practice. This article argues that our current understanding of journey to crime is incomplete. It improves our understanding by resolving a fundamental unit of analysis issue that had thus far not received much attention in the literature. It is demonstrated that the aggregate distribution of crime trips (commonly known as the distance decay) does not take into account the considerable variation that exists between individual offenders’ crime trip distributions. Moreover, the common assumption of statistical independence between observations that make up a distribution is something that, until now, has yet to be tested for distributions of crime trips of multiple offenders. In order to explore these issues, three years of burglary data from a UK police force were linked to 32 prolific offenders to generate journey to crime distributions at the aggregate and offender levels. Using multi-level models, it was demonstrated that the bulk (65%) of the variation of journeys to crime exists at the offender level, indicating that individual crime trips are not statistically independent. In addition the distance decay pattern found at the aggregate level was not, in the main, observed at the offender level – a result that runs counter to conventional wisdom, and another example of the ecological fallacy. The implications of these findings are discussed.

On the electrical characteristics of latent finger mark corrosion of brass

Apparatus constructed to measure the variation (ΔV) in applied potential (V) over the surface of brass discs subject to corrosion by latent finger mark deposits is described. Results show values of ΔV of up to 14 V for V = 1400 V on regions of disc coincident with the location of finger mark corrosion. Measurement of ΔV for 0 V ≤ V ≤ 1400 V has revealed a non-linear relationship, which is very similar to that measured for a commercial metal–semiconductor Schottky rectifier. Further experiments have shown the corrosion product on the brass to be a p-type semiconductor with current/voltage characteristics for the brass-corrosion contact consistent with the characteristics expected for a rectifying metal–semiconductor contact. The composition of the semiconductor is discussed in terms of metal oxide corrosion products with p-type copper (I) and copper (II) oxides thought most likely to be responsible for the semiconductor behaviour of the corrosion product. A simple model is described for the galvanic corrosion of brass by finger mark deposits that is consistent with the experimental results.

Behavioural case linkage with solved and unsolved crimes

Offender behaviour is used to distinguish between crimes committed by the same person (linked crimes) and crimes committed by different people (unlinked crimes) through behavioural case linkage. There is growing evidence to support the use of behavioural case linkage by investigative organisations such as the police, but this research is typically limited to samples of solved crime that do not reflect how this procedure is used in real life. The current paper extends previous research by testing the potential for behavioural case linkage in a sample containing both solved and unsolved crimes. Discrimination accuracy is examined across crime categories (e.g. a crime pair containing a car theft and a residential burglary), across crime types (e.g. a crime pair containing a residential burglary and a commercial burglary), and within crime types (e.g. a crime pair containing two residential burglaries) using the number of kilometres (intercrime distance) and the number of days (temporal proximity) between offences to distinguish between linked and unlinked crimes. The intercrime distance and/or the temporal proximity were able to achieve statistically significant levels of discrimination accuracy across crime categories, across crime types, and within crime types as measured by Receiver Operating Characteristic (ROC) analysis. This suggests that behavioural case linkage can be used to assist the investigation, detection and prosecution of prolific and versatile serial offenders.

Visualization of latent fingerprint corrosion on a discharged brass shell casing.

Abstract:  Latent fingerprint visualization on discharged shell casings can provide good forensic evidence, particularly if the casing is recovered at the scene of a crime where a firearm has been discharged. Unfortunately, visualization of such latent fingerprints when they were deposited prior to discharge of the firearm is problematic as both increased temperature and abrasive friction can inhibit fingerprint visualization with conventional techniques. We present a case study that demonstrates latent fingerprint visualization on a discharged shell casing recovered 14 years ago from the scene of a homicide. Previous cyanoacrylate fuming of the casing had failed to reveal any fingerprints. We use a visualization technique in which a conducting carbon powder adheres preferentially to latent fingerprint corrosion of the casing surface, following the application of a potential of 2.5 kV to the casing. This technique presents opportunities for the review of old cases and for consideration of its use in current cases.