Tracers as invisible evidence - The transfer and persistence of flock fibres during a car exchange.

This study assessed the recovery of flock fibres used as a tracer in a car exchange scenario. Flock fibres were deposited onto a car seat (or model thereof) and their transfer and persistence was investigated after a real or simulated car exchange. The overall aim of this study was to achieve an optimal use of flock fibres as tracers, i.e. to be able to select a fit-for-purpose flock fibre, to be able to predict the amount of flock fibres to be recovered from crime related items, and to be able to use these numbers to exclude accidental uptake. The effect of a number of variables on the transfer and persistence of flock fibres was studied, including flock fibre length, car upholstery, and trousers material. Laboratory based experiments were undertaken first, followed by realistic field based experiments. The flock fibres were captured in a non-destructive manner through fluorescence photography. A Matlab algorithm enabled fast automated counting of flock fibres on the images. Results indicate that an initial rapid loss of flock fibres from garments may be expected as a result of moderate movement. Although the amount of flock fibres to be recovered is affected by the flock fibre length, the type of car upholstery, and the type of trousers materials (if frictional force is taken into consideration), large numbers of flock fibres have been recovered from all target materials throughout the transfer route. These numbers are higher than the amount of flock fibres recovered due to accidental uptake. In conclusion, flock fibres can serve as invisible evidence to reconstruct a series of events.

The possibilities and limitations of forensic hand comparison.

On recordings of certain crimes, the face is not always shown. In such cases, hands can offer a solution, if they are completely visible. An important aspect of this study was to develop a method for hand comparison. The research method was based on the morphology, anthropometry, and biometry of hands. A new aspect of this study was that a manual and automated test were applied, which, respectively, assess many features and provide identification rates quickly. An important observation was that good quality images can provide sufficient hand details. The most distinctive features were the length/width ratio, the palm line pattern and the quantity of highly distinctive features present, and how they are distributed. The results indicate that experience did not improve the identification rates, while the manual test did. Intra-observer variability did not influence the results, whereas hands of relatives were frequently misjudged. Both tests provided high identification rates.