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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