Crime scene integrity

The collection of physical evidence is not generally considered time sensitive however, site characterization and sampling activities are time sensitive due to the public health implications of contaminated environmental media air, water, and/or soil. Thus, collection of environmental media samples may precede collection of physical evidence, and care must be taken not to disturb the crime scene while performing these activities. If samples can be collected outside of the boundaries of the suspected crime scene, this may avoid concerns about the integrity of the crime scene. 

Discuss principles related to an MCI site as a crime scene, for example, maintaining integrity of evidence, chain of custody. 

The chemical characterization of forensic evidence from a crime scene or the criminal has some different requirements from that of many other types of chemical analysis. High sensitivity is important because the quantity of material for examination is often limited to minute traces found at the scene. The material under scrutiny must be characterized as comprehensively as possible to ensure maximum discrimination from other material in the same class. Forensic laboratories are multiinstrument facilities required to deal with many types of evidence found at a crime scene therefore, the routine methods used should preferably employ relatively inexpensive instrumentation. In order to protect integrity, samples should be analyzed as received if possible and any workup minimized. The method should preferably not be labor intensive. Pyrolysis-gas chromatography (Py-GC) and pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS) have proven to be an effective means of satisfying these requirements in many forensic science laboratories. - ... 

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