During a robbery, the victim is restrained with tape. Later, a suspect is identified based on tactical information and taken into custody. The blue polyester gloves found in the suspect's pocket and the tape recovered from the victim are sent to the lab for examination. During the laboratory analysis, a clear glove-print is observed on the tape. Fibres from this Vismodegib print are isolated and match the fibres from the suspect's gloves.
In this case a single reference material is related to a single type of fibre traces. The proposed source level hypotheses are:Hp: The gloves are the source of the fibres isolated from the tape.Hd: Another textile is the source of the fibres isolated from the tape.
The following symbols are proposed to facilitate the derivation:r: the gloves (i.e. the obtained reference material) contain fibres of type r;k: the trace fibres (i.e. material recovered from the tape) are of type k; We explicitly assume that all fibre traces of the same type originate from the same source.E: the evidence, comprising both the classifications of r and k and a match between these fibres, or r = k;πj: the frequency of fibre type j, defined as the probability that an arbitrary item within a relevant population contains matching fibres.