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Evidence Collection

excerpted from "Motive, Means, and Opportunity, A Guide to Fire Investigation."
American Re-Insurance Company, Claims Division, 1996.


Table of Contents


Introduction

THE READER IS URGED TO CONSULT APPROPRIATE LEGAL COUNSEL FOR THE LAW, POLICIES AND PROCEDURES APPLICABLE IN YOUR JURISDICTION.

There are several types of evidence. Understanding the differences is critical to the effectiveness of an arson investigator--

Physical Evidence - Evidence of a fact which has physical existence, not just a mental concept. In arson, physical evidence could be a container of flammable liquid, a trailer or an incendiary device.

Direct Evidence - Evidence that proves a fact in question. An example would be an eyewitness to the fire being started.

Indirect (or Circumstantial) Evidence - Evidence of facts or circumstances from which the existence or non-existence of a fact in question can be inferred. An example would be a fire fighter's testimony that he found a container with what he thought was gasoline at the scene, and a lab confirming that the container held gasoline.

1. Physical Evidence Collection

Blood:

Liquid

  • collect and place blood in a clean glass stoppered container
  • refrigerate and deliver to the lab A.S.A.P.
  • EDTA ("purple cap") blood collection tubes are best - especially for DNA samples
  • articles bearing wet blood (garments, carpet) should be placed on a clean surface to air dry - never collect a wet garment in a sealed, airtight container or plastic bag -this retains moisture, promotes bacterial growth and sample deterioration

Dry

  • submit whole article to lab or cut out the portion containing the stain
  • if stain is on a solid object, which can't be taken, document and sketch the bloodstain pattern and then scrape the stain off onto a clean piece of paper using a clean razor blade
  • if stain can not be scraped, it may be eluted onto clean, cotton threads moistened with sterilized saline (or water) by rubbing the threads on the stained area
  • threads are then allowed to dry and should be placed into a paper fold packet

Clothing:

  • if wet with blood or other body fluids, air dry at room temperature-don't accelerate drying with a fan or heater
  • label with identifying data and place in paper, using additional paper between folds - DO NOT USE PLASTIC BAGS

Charred Documents:

  • if documents are in a container, package the entire container to submit to the lab
  • if documents are loose, slip cardboard under the document(s) and place in a container partially filled with cotton to restrict movement
  • package and transport to lab

Documents/Checks:

  • place in plastic envelope using tongs or tweezers
  • seal plastic envelope and label it
  • DO NOT HANDLE THE DOCUMENT WITH FINGERS - FINGERPRINT EVIDENCE WILL BE DAMAGED

Fingerprints:

Latent

  • immobilize article to prevent friction on the fingerprint bearing surface
  • submit the entire article to the lab

Visible

  • photograph and submit entire article to lab
  • DO NOT ATTEMPT TO PROCESS BY DUSTING WITH FINGERPRINT POWDER

Footprints:

  • photograph each print located
    • place ruler or other scaler identification next to the print
    • take photo holding camera directly over impression, illuminating it with a detached flash or strobe light, low and to the side of the impression
  • prepare plaster or other casting material and make plaster impressions (if inexperienced, practice on your own footprint first - once cast is made the impression is destroyed)
  • scratch initials, date and exhibit number into the back of the cast when it's dry u scratch a directional arrow pointing NORTH on the back of the cast
  • follow directions for packaging plaster casts

Glass:

  • package in paper
  • protect broken edges - a physical match may be possible
  • put wrapped glass in labeled solid protective container

Hair and Fibers:

  • place samples in paper folded in the "Druggist Fold"
  • place paper in envelope and seal
  • label envelope

Paint:

  • place samples in paper folded in the "Druggist Fold"
  • large chips should be protected in a pill box or other protective container - a physical match may be possible

Plaster Casts:

  • package in a large, firm container using newspaper to cushion and prevent breakage
  • don't attempt to clean the bottom of the cast - it may be damaged
  • identifying data should be marked into the cast before it hardens

Soil/Safe Insulation:

  • place in metal pint containers
  • label should include the exact location of the origin of the sample

Tire prints:

  • photograph each print located
    • place ruler or other scaler identification next to the print
    • take photo holding camera directly over impression illuminating it with a detached flash or strobe light, low and to the side of the impression
  • prepare plaster or other casting material and make plaster impressions (if inexperienced, practice on your own tire print first - once cast is made the impression is destroyed)
  • scratch initials, date and exhibit number into the back of the cast when it's dry u scratch a directional arrow pointing NORTH on the back of the cast
  • follow directions for packaging plaster casts

Firearms:

  • unload weapon - be careful not to ruin possible latent fingerprints
  • note manufacturer's name, caliber, model, serial number and presence of ammunition and shell casings
  • immobilize weapon - mount it on cardboard with string and transport to lab
  • WEAPON SHOULD BE HANDLED BY THE CHECKERED GRIPS OR EDGES OF THE TRIGGER GUARD

Bullets (all types - live and not live rounds) and Cartridge Casings:

  • DO NOT MARK IN ANY WAY. Package each bullet SEPARATELY and label

Tools (i.e., as a piece of physical evidence):

  • tool edges should be protected by wrapping in newspaper
  • udentifying information should be on a tag attached to the tool
  • for tool marks - remove the entire article or cut out the portion containing the mark
  • if neither option is possible - make a silicone case of the mark

2. Trace Evidence*

Trace evidence is material or clues (other than accelerant samples) that help point toward a suspect( s) or motive(s), or the cause and origin of the fire.

Trace evidence includes-

  • Serological samples (blood, hair and skin). Can be used to determine blood type or a DNA "fingerprint" can be determined. These samples are often vital for identifying and/or eliminating arson suspects.
  • Questioned documents (financial records, checks, letters, business papers, insurance policies, securities and property records). In addition to their actual content, when, why and how documents were prepared provides valuable information about cause and origin, motive(s), and suspects.
  • Latent fingerprints. Latent fingerprints can actually be recovered from Molotov cocktails, accelerant containers and failed incendiary devices. Even a small fragment of the device or container damaged in the fire can provide enough information for a positive identification of an arson suspect.
  • Device remnants (pipe parts, machine or appliance parts, wire or metal samples). Forensic labs often keep files of materials used in the manufacture of incendiary and explosive devices. Device remnants or small fragments can be identified by matching them to undamaged original pieces in the files.
  • Maintenance manuals have been used to identify appliance parts. Wire and metal give clues about heating or temperatures at different points in the fire. This category of evidence also includes common consumer products like swimming pool disinfectant, hair gel, soap powder, brake fluid and road flares that can all be used to create chemical incendiaries. Residues of these substances provide clues to the cause of ignition.
  • Tool Marks. Implements used to pry open doors, windows or cabinets, or to lift or cut items leave characteristic marks. These marks can identify the tool used and eliminate from evidence damage caused by fire fighters. Marks on bodies can also be identified.

Trace evidence can be difficult to collect because-

  • There is usually such a small amount among the useless fire debris.
  • Determining what will be valuable is difficult.
  • Destructive overhaul practices can destroy evidence and produce excess debris.
  • Even sieving debris (often used in the field) can damage brittle specimens.

3. Fingerprint Collection-Special Handling

Proper collection of fingerprints demands special techniques. Prints are either lifted at the scene or preserved for latent fingerprint analysis.

When a fingerprint is found on the suspected ignition device (e.g., Molotov cocktail container), both the fingerprints and the accelerant inside the container are needed as samples. Prints can be lifted at the scene and the container sent to the lab, or the accelerant is decanted into an evidence container and the fingerprint is preserved for separate analysis later. The preferred method is the latter.


*This section is based upon, and contains excerpts and quotes from, "Arson Investigation," by Dr. Henry C. Lee and is used with his permission.

Reprinted with permission.

 
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