Contamination of Evidence
The unwanted alteration of evidence is contamination and it affects the integrity
of the original exhibit or the scene of crime. Contamination of evidence may
link a civil person to scene of crime and may lead to a guilty individual not being
charged. Effects of contamination is
1) Original evidence transfer wiped up due to unwanted
alteration
2) Contamination dilute a sample,
3) Deposition of misleading new materials onto an exhibit.
All these effects compromise the analysis of the original evidence and resulted
that the court may not accept the analysis.
There are number of ways a Contamination can take place -
During a tactical investigative response Police or other first responders interfering with the evidence.
In a process of covering up or removing evidences, suspects
interfere with the crime scene.
Unknowingly handling of evidence by victims or witnesses.
Unwanted transfer of evidence or even elimination of evidence by animals (Pets) through contact or
consumption.
Weather also causes contamination due to rain, wind, or snow resulted in diluting or washing away
evidence.
During investigation, Investigators Oblivious to follow proper scene of crime management procedures
and initiating contamination of
exhibits or cross-contamination between exhibits.
The court will agree that when issue of life and safety are at risk, some contamination is not under the
control of investigator. Once the crime scene is locked down, crime scene management procedures
must be put in
place.
Challenge for investigators, is how to...
1) Prevent contamination
2) Control ongoing contamination, and
3) Record the known contamination that has taken place.
To determine/establish the dimension and to protect the crime scene should be the first priority as it
reduces the risk of contamination.
1) Crime scene contamination - The actions of the personnel at
the crime scene are usually results in contamination of the scene. The
scene/evidence will be contaminated by presence of more personnel at the scene.
The deposition of hairs, fibers and other trace evidences take place from the
clothing of scene personnel or even destroying of fingerprints and shoes/foot
prints.
2) Degree of contamination - The type of crime scene is related
to the degree of contamination as for EX. In a theft case less number of
individuals has access to the scene as compared to a typical death scene.
Higher number of individuals has access to crime scene; the potential for contamination
is always higher.
3) Environmental factors: Environmental conditions play major
role in the contamination of crime scene evidence specially the outdoor crime
scene. For EX. blood evidence at an outdoor crime scene and it rains, then the
blood may become diluted. Wind may blow away evidence or can carry
contamination. Wind, sun, rain, snow and temperature play significant role in
the contamination or destruction of the evidence at a scene of crime.
4) Equipment - The equipment used at scene of crime is also a
source of contamination (equipment used for photography, sketching equipment
and all processing equipment in crime scene kits). We can controlled this
contamination by decontaminate the equipment before use.
How is contamination of evidence reduced?
Following steps should be taken to prevent contamination –
1) Locking down the Crime Scene or protecting the crime
scene
Protecting the crime scene prevent the risk of
contamination. First priority should be given to determining the dimension of the crime scene. Indoor crime scene is easier to secure in comparison to outdoor
crime scene. Weather conditions and crowd is responsible for contamination in
outdoor crime scene. Isolating the crime scene inside a perimeter is locking
down. Stop all ongoing activities inside the crime scene, everyone should be
out and a physical barrier, police tape or rope, is placed around the outside
edges of scene of crime.
Next step after locking down is to establish a designated
pathway from where authorized personnel can re-enter the scene of crime.
Photography is must prior to re-enter the crime scene.
How to protect crime scene, link below
https://www.forensicfingerprint.in/2020/05/crime-scene-investigation-series-5.html
2) Loss of Continuity
Establish and maintain continuity of evidence is must like
controlling contamination. Chain of custody is essential and helps to reduce
contamination.
Crime scene personnel must follow a protocol for evidence
collection to reduce contamination. The order of evidence collection is to
collect the large articles first then recover the trace like hairs and fibers,
then further collect the biological fluid, tool marks, visible finger prints or
footwear patterns and on last latent impressions.
As discuss earlier it is advisable to minimize direct contact
with exhibits by wear barrier clothing, less number of people at scene of
crime, cleaning and/or sterilizing of equipment. Barrier clothing includes face
mask, hair cover, gloves, etc.
3) Packaging and Collection
Packing of evidence is an essential part of scene of crime
and it prevent destruction and contamination of evidence. Always used new and
clean container to pack evidence, some evidence required sterile containers.
The containers must be sealed at the crime scene.
How to pack physical evidence link below-
https://www.forensicfingerprint.in/2020/06/packaging-of-physical-evidences-at.html
4) Transporting Evidence
Biological evidence is sensitive to temperature, so they
require consideration to prevent destruction and contamination. Precautions to
prevent freezing of the evidence should also be taken during winter times.
Carelessness during transportation/storage of evidence leads to contamination
or destruction of evidence.
Conclusion
Contamination of evidence has been a concern for law enforcement
and forensic personnel. If evidence is collect properly, pack and handle
correctly during transportation and storage, the potential for contamination
will be greatly reduced. It resulted in saving the integrity and value of the
evidence for further process.
MR. DEEPAK PAWAR has been working as Finger Print Expert / Police Officer in Finger Print Bureau , Delhi Police at New Delhi since 2001 . He is the senior most Finger Print Expert , attending / visited several scene of crime and solved many crime cases .He has passed M.Sc (Chemistry) and he is the Member of International Association of Identification . He is the Member of Delhi Police welfare association . He is supervising the Forensic , New Delhi District , Mobile Crime Team . He is one of the Expert in the Special Investigation Team held for investigation of important cases . He has been giving fingerprint proficient training to Delhi Police personnel's . He has been Presented / giving lectures on topics related to forensic science . He is also making examination paper of Finger Print proficient course . He is awarded with Police Medal by MHA and Delhi Police.