October 1999 Volume 1 Number
3
1.0. Scope
This guide describes procedures
and techniques for the documentation, detection, collection,
and preservation of trace evidence from crime scenes, individuals,
and items submitted to the laboratory for examination.
2.0.
Significance and Use
Locard's Exchange Principle
states that whenever two objects come into contact, a transfer
of material will occur (1). Trace evidence that is transferred
can be used to associate objects, individuals, or locations.
2.1. The integrity and significance
of trace material as associative evidence relies on proper detection,
collection, and preservation.
2.2. An understanding of
the transfer and persistence of trace evidence will assist the
examiner in interpreting the significance of the analytical results.
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3.0.
Documentation
3.1. When a case is initiated,
a file specific for that case must be created to contain the
case documentation for the length of time required by the prevailing
laws and nonconflicting agency policy.
3.2. Documentation of questioned
and known trace evidence collection, whether done in a laboratory
or at a scene, must include permanent notes about
a. date (and time, when appropriate)
of the collection,
b. name of person or persons
collecting the evidence,
c. a descriptive listing
of item or items collected,
d. a unique identifier for
each item collected such as an item number and case number, and
e. location of each item
(documented by notes, sketches, measurements, photographs, or
a combination of these).
3.3. The chain of custody
for each item must be initiated upon collection and maintained
until final disposition.
3.4. Recommended procedures
for documenting and labeling physical evidence are outlined in
ASTM Standard E 1459-92, Standard Guide for Physical Evidence
Labeling and Related Documentation (9.2), and Standard E 1492-92,
Standard Practice for Receiving, Documenting, Storing, and Retrieving
Evidence in a Forensic Science Laboratory (3).
3.5. The principles of record
initiation, maintenance, storage, and security are fundamentally
the same for evidence collections within the laboratory and collections
that may begin at a site remote from the laboratory.
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4.0.
Contamination and Loss
4.1. When collecting or examining
items, care must be taken to prevent contamination and loss of
trace materials.
4.2. If a case involves disciplines
other than trace evidence, the involved examiners should confer
before any work is undertaken. Unless circumstances dictate otherwise,
the trace evidence should be collected and preserved prior to
other examinations.
4.3. General principles and
practices to avoid evidence contamination and loss, applicable
to both laboratory and nonlaboratory settings, include the following:
4.3.1. Contact between items
and personnel before the appropriate trace evidence has been
secured should be restricted.
4.3.2. Appropriate protective
apparel, such as laboratory coats and disposable gloves, must
be worn to prevent contamination from the clothing of the examiner.
The apparel must be changed as necessary to avoid contamination
or transfer between evidentiary items, locations, and personnel.
4.3.3. Items being collected
for trace evidence examination must be handled as little as possible
to minimize loss of the trace evidence and to limit exposure
of the items to contaminants.
4.3.4. Collect, package,
and seal items individually in appropriate packaging. Keep items
in a secure, sealed package until the item is processed in a
controlled environment.
4.3.5. Equipment and work
surfaces used during collection and examination must be cleaned
in an appropriate manner before processing begins and as often
as necessary during processing to prevent contamination.
4.3.6. Adhesive lift materials
(used for collection, storage, or both) must be maintained in
a manner to avoid contamination. Caution should be used to prevent
tape edges from contacting any uncleaned surfaces.
4.3.7. Evidence examination
areas should have adequate lighting, easily cleaned surfaces,
and a physical environment designed to restrict excessive air
currents, static electricity, and general foot traffic.
4.3.8. The examination of
questioned and known items for trace evidence must be conducted
separately in different locations, at different times, or both,
to prevent contamination. It is recommended that questioned items
with the most probative value be examined first.
4.3.9. Any contact, condition,
or situation that could cause contamination or otherwise compromise
the trace evidence examination must be documented and communicated
between the laboratory analyst or analysts and the submitter.
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5.0. Detection, Collection, and Preservation
Techniques
5.1. When selecting detection,
collection, and preservation methods and the processing sequence,
consider the circumstances of the case, ambient conditions, the
discriminatory power of the different techniques, and the need
to preserve or collect other types of evidence.
5.2. Record the techniques
used for detection, collection, and preservation of the evidentiary
items and the location from which they are removed.
5.3. Methods used for detecting
trace evidence include but are not limited to general visual
searches; visual searches assisted by different types of illumination,
such as oblique lighting and alternate light sources (UV, laser,
high intensity); and visual searches assisted by magnification.
5.4. Trace evidence recovery
or collection techniques used should be the most direct and least
intrusive technique or techniques practical. Collection techniques
include picking, lifting, scraping, vacuum sweeping, combing,
and clipping.
5.4.1. Picking. Trace
evidence may be separated from an item by using clean forceps
or other implements. The collected samples should be immediately
protected against loss or contamination.
5.4.2. Lifting. An
adhesive-bearing substrate such as tape is repeatedly and firmly
patted or rolled over the item causing loosely adhering trace
evidence to stick to the tape. Do not overload the tape. The
collected lifts are typically placed on a transparent backing
(e.g., clear plastic sheeting, glass slides, and clear plastic
or glass petri dishes). This protects against contamination and
permits samples to be easily viewed and removed for further comparison.
5.4.3. Scraping. A
clean spatula or similar tool is used to dislodge trace evidence
from an item onto a collection surface such as clean paper. The
collected debris is immediately packaged in a manner to avoid
sample loss. This technique is most often conducted within the
laboratory in a controlled environment that reduces the risk
of contamination or loss of the trace evidence.
5.4.4. Vacuum Sweeping.
A vacuum cleaner equipped with a filter trap is used to recover
trace evidence from an item or area. The filter and its contents
should be immediately packaged to avoid sample loss. The appropriate
vacuum parts, filter, and trap must be changed and rigorously
cleaned between each vacuuming to avoid contamination. Consider
using this method subsequent to other collection techniques as
it is indiscriminate and may result in the collection of a large
amount of extraneous material.
5.4.5. Combing. A
clean comb or brush is used to recover trace evidence from the
hair of an individual. The combing device and collected debris
from the hair should be packaged together.
5.4.6. Clipping. Trace
evidence can be recovered from fingernails by nail clipping,
scraping, or both. Fingernails may be clipped with clean scissors
or clippers and packaged in clean paper. Fingernails may be scraped
with a clean implement to collect debris from under the fingernails.
Package the collected debris and the scraping device as one unit,
typically in clean paper. Commonly, fingernails from the right
and left hands are packaged separately. This does not preclude
the collection of each or any nail separately from all others,
such as a nail with obvious damage.
5.5. Appropriate preservation
and packaging of trace evidence and items to be examined for
trace evidence will vary. Appropriate packaging must prevent
loss or contamination of the trace evidence.
5.5.1. All evidence packages
must be properly sealed in a manner to prevent tampering and
eliminate loss or contamination of the trace evidence through
open edges.
5.5.2. Small or loose trace
evidence must be secured in clean, unused primary containers
such as paper packets or petri dishes. The primary container
should then be appropriately secured in an envelope or paper
bag.
5.5.3. Large items, such
as whole garments, should preferably be sealed individually in
clean, unused packaging.
5.5.4. Clothing and other
items that are wet must be air dried as soon as possible, without
exposure to heat or sunlight, in a secured area in a manner that
will prevent loss or contamination of trace evidence. An arrangement
to collect any trace evidence that may fall from the item during
drying should be used.
5.5.5. Small or manageable
items at a crime scene that bear visible, firmly attached trace
evidence should be documented, packaged intact, and transported
to the laboratory for examination.
5.5.6. Items at a crime scene
that bear visible but easily lost trace evidence or items that
are impractical to transport should be documented and the trace
evidence collected by an appropriate technique.
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6.0. Site and Special Collection Considerations
6.1. Personnel responsible
for the detection and collection of trace evidence should be
aware of the applicable laws governing search warrants, searches,
and seizures within their jurisdiction.
6.2. Personnel should be
aware that various types of evidence will be present during the
processing of a crime scene or the examination of items submitted
to the laboratory. Some types of evidence other than trace evidence
may be more significant to a particular case and therefore should
be given higher priority.
6.3. Representative known
samples of an item, sufficient to represent all variations that
may be present within that item, should be collected for comparison
with the questioned trace evidence. The areas from which these
samples are collected must be documented.
6.4. Patterned marks or impressions
may be encountered and may require additional documentation and
collection procedures such as 1:1 scale photography. Enhancement
techniques such as oblique lighting or powder dusting and preservation
techniques such as adhesive lifting or casting should be considered.
6.5. The possibility of physically
matching a fractured, broken, torn, or cut portion of an object
to its source should always be considered. The entire questioned
item and possible source item should be collected, protecting
the edges from further deformation. When the possibility of a
physical match exists, one should not overlook the necessity
of maintaining all items separately to prevent contamination.
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7.0.
Evidence Security
7.1. Trace evidence shall
remain in secure, controlled-access areas, protected from loss,
damage, or contamination. It must have a documented and continuous
chain of custody from the time of evidence collection until the
time the evidence is admitted into court or the case has been
disposed and the evidence is no longer needed.
7.2. The security and integrity
of evidence is the responsibility of all persons who may identify,
collect, package, store, transport, or examine evidentiary items.
7.3. Procedures and techniques
for the identification, storage, and retrieval of evidence in
a forensic science laboratory are outlined in ASTM Standard Practice
E 1492-92, Standard Practice for Receiving, Documenting, Storing,
and Retrieving Evidence in a Forensic Science Laboratory.
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8.0. Training Requirements for Trace Evidence
Collection Personnel
8.1. The responsibility of
trace evidence collection may be assigned to personnel of varying
occupations and levels of expertise such as crime scene technicians,
law enforcement personnel, and medical personnel. These personnel
must be trained in trace evidence detection, collection, and
preservation techniques.
8.2. Training should include
but not be limited to the record-keeping protocol of the agency;
crime scene search techniques; rules of evidence handling; safety
concerns of evidence handling and detection techniques; legal
aspects of search warrants, seizures, and evidence recovery;
chain-of-custody requirements; storage of physical evidence;
the detection, collection, and preservation methods used for
trace evidence; contamination prevention; and the significance
of trace evidence analysis results.
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9.0.
Referenced Documents
1. Locard, E. The analysis
of dust traces. Part I. American Journal of Police Science
(1930) 1:276-298.
2. ASTM E 1459-92: Standard
Guide for Physical Evidence Labeling and Related Documentation.
American Society for Testing and Materials, West Conshohocken,
Pennsylvania.
3. ASTM E 1492-92: Standard
Practice for Receiving, Documenting, Storing, and Retrieving
Evidence in a Forensic Science Laboratory. American Society
for Testing and Materials, West Conshohocken, Pennsylvania.
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10.0.
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