Evidence Collection & Preservation Flashcards

When should an investigator stop collecting evidence from a fire scene and obtain a warrant?

Answer: When the owner or occupant objects to the continued search

Per Michigan v. Tyler and Michigan v. Clifford, once the emergency ceases and the owner objects, investigators must obtain a warrant to continue searching.

Which accelerant detection method is used by investigators in the field to get a preliminary indication of ignitable liquid presence before lab analysis?

Answer: Portable hydrocarbon detector or combustible gas indicator

Portable hydrocarbon detectors provide field-level screening for ignitable liquid vapors, though lab GC-MS is required for definitive identification.

An investigator collects soil samples from outside a structure where runoff from firefighting may have carried accelerants. What is the main concern with these samples?

Answer: Water dilution and soil composition may affect the concentration and detectability of accelerant residue

Firefighting water runoff can dilute accelerant residue and soil composition can naturally contain hydrocarbons, both of which affect laboratory interpretation.

What is the significance of documenting witness statements as part of evidence preservation in a fire investigation?

Answer: Witnesses can identify pre-fire conditions, behavior of the fire, and potential suspects that physical evidence alone cannot establish

Witness statements document observations about pre-fire conditions, fire development, and persons present that physical evidence cannot capture and are critical to establishing motive and timeline.

If an investigator must collect evidence from a vehicle fire, which area should be sampled for ignitable liquid residue if arson is suspected?

Answer: Trunk lining and floor mats in the passenger compartment

Trunk linings and floor mats in the passenger compartment are common targets for accelerant application in vehicle arsons and should be sampled.

Which of the following is a proper technique for collecting a dry debris sample suspected of containing accelerant residue?

Answer: Use a clean, stainless steel tool to transfer material into a clean, lined or unlined paint can and seal immediately

A clean metal tool and an airtight metal or glass container are used to prevent contamination and volatilization of any accelerant residue in the sample.

During evidence packaging, why should containers for ignitable liquid evidence NOT be filled completely to the top?

Answer: Headspace above the sample allows volatile compounds to vaporize, making collection by the lab easier and more accurate

Leaving headspace allows volatile accelerant residue to vaporize into the container's air space, which the lab draws off with a syringe for GC-MS analysis.