Traces and samples of geological materials are sources of evidence and, like all other types of evidence, must be collected by experts in forensic techniques and stored appropriately, respecting codified international procedures .
The value of comparability between samples of geological materials largely depends on the way they were collected and stored, as well as on the preliminary assessments made in the analysis phase of the crime scene. For this reason, the collection of geological materials requires a logical sequence of operations which must be videos or photos documented in each phase.
The collection of evidence can be carried out with the application of different methodologies that must comply with strict procedures, codified at the international level. Regardless of the method applied, the collection and conservation of evidence must be extremely accurate, avoiding possible contamination and alteration of the traces and adopting particular precautions that are different depending on the material to be collected.
Experts should always wear personal protective equipment and use disposable collection tools for each sampling.
After the collection, the chain of custody of evidence must be ensured, which is a set of procedures that ensure both the identification and the integrity of evidence during all stages of processing, from the collection of traces on the scene of the crime to laboratory, until their final delivery to the Judicial Authority. The chain of custody consists in tracing, with appropriate paper, digital and photographic documentation, the sealing and opening of the packages containing the evidence, the processing phases as well as the operators involved.
The suitable collection of evidence and their optimal conservation, through right procedures, guarantee the probative validity of the information obtained in the analytical phases.