Method of residue analysis:
(1) Items are collected from the scene as soon as possible after the explosion and sealed in air-tight containers.
(2) In the laboratory the closed container is heated in order to release volatile chemicals.
(3) The heated air is suctioned out of the container through activated charcoal that traps the volatile chemicals.
(4) The chemicals are extracted from the charcoal and analyzed (gas chromatography - mass spectroscopy or other suitable instrument).
Analysis of the residue:
(1) can help to determine the most likely cause
(2) can exclude possible explanations
Causes of false negative analysis:
(1) delay in scene analysis allows volatile chemicals to dissipate into the environment
(2) degradation of the chemicals by oxidation, heat, etc
(3) washing away of residues by water
(4) technical factors (instruments failure, analyst inexperience)
Causes of false positive analysis:
(1) contamination of the site by other explosives
(2) intentional addition of material by the perpetuator to mislead
