A model for the evidence dynamics of forensic trace materials #

Gareth Jenkins, Helen Wilson, Ruth Morgan

11:30 Wednesday in 4Q07.

Part of the Granular and multiphase flows session.

Abstract #

Microscopic particles of contraband materials can be deposited onto surfaces via fingerprints, and these trace evidence samples can then be analysed to infer key details of suspected criminal activities. A forensic reconstruction such as this will be more robust if we can develop an understanding of how these materials behave.

Suppose, for example, that an investigation is carried out around a crime scene involving the handling of a particular contraband material, and a series of prints are found and analysed with varying quantities of the material identified in each. The investigation then wants to know the order in which these prints were made, but there are uncertainties in determining this. Can we reliably assume that the amount of transferred material will decrease monotonically in each print? To what extent do the physical properties of the contraband and the imprinted surfaces affect this reliability?

We are working towards a model which can replicate the transfer patterns found in experimental data of crystalline explosive particles. We use a coarse-grained model for the crystalline particles, approximating them as aggregates of elastic spheres with breakable bonds.

In this talk we cover the methodology of this model, show simulations which demonstrate various desired behaviours of the evidence particles, and discuss early insights made about their transfer patterns.