CHAPTER 2: Degradation and Damage due to Exposure to Light in Trace Evidence

All actions leave traces, and thus material evidence such as paint, textile fibres, glass fragments, etc. are very informative mute witnesses which can help investigators reconstruct the dynamics of crimes.

In many instances, the forensic scientist is required to compare items coming from the crime scene with objects which are their possible sources. A typical example is when textile fibres found on a dead body are compared with the garments of a suspect. If it can be concluded that the fibres indeed came from the clothing of the suspect, a connection between them and the crime scene can be made. Depending on the context, this can make a difference between apprehending and convicting a felon or leaving a case unsolved. Needless to say, it is paramount that conclusions are taken on solid and objective evidence. When traces have been exposed for long times to weathering, degradation, especially by light, their structure can be modified which can complicate the work of the analyst.

In this chapter, the issues related to degradation of material evidence found on the crime scene are discussed. Polymeric evidence is focused on, because polymers are the traces most sensitive to degradation, whereas glass, soil, or other materials are not significantly changed by exposure to the elements for the times involved in normal casework.