Biological evidence at the crime scene is the samples of
biological material such as
• Blood
• Semen
• Saliva
• Urine/Feces
• Hair
• Teeth/Bone
• Tissue
• Cells
Each crime scene investigation is based on the theory of transfer or exchange
established by Edmond Locard, a Frenchman, that state that every contact leaves
a trace. This exchange involve, hairs, dirt, dust, fibers, blood and other bodily
fluids, skin cells, metallic residue and other microscopic constituents. The motive
is to establish a link between the crime scene, the victim, physical evidence,
and the criminal/suspect.
Biological evidence is essential in linking someone to or excluding someone from
crime scene. It helps the criminal justice system to reach a conclusion about the
guilt or innocence of the suspect. It is necessary that it has been properly preserved,
processed, stored, and avoided to be contaminated, loss, premature destruction or
degradation.
DIRECT TRANSFER
Transfer of material from the original source to another
person or object is a direct transfer.
Example -
1) Victim’s blood present on the suspect clothing.
2) Suspect’s semen recovered from the victim.
INDIRECT TRANSFER
Trace evidence, first directly transferred to one location
and then transferred again to another location is an indirect transfer.
Example –
Rug fibers at scene of crime had been transferred to victim
cloth and then found in the offender car after he transported the body.
Solid state evidence adhered while liquid biological
evidence absorbed.
Evidence collection -
Biological evidence is subject to deterioration. It must be
carefully collected and preserved, so that useful information can be obtained
from its analysis and used for legal system.
The collection method of biological evidence depends largely
on the state and condition of the evidence.
When we collected biological evidence for DNA analysis, a
significant quantity of material should be collected for testing purposes.
Biological specimen after collection should be promptly delivered to the
forensic laboratory. Items should be stored in a cool, dry atmosphere to
minimize sample deterioration, until they are submitted for testing.
Samples must be frozen or dried; there are chemical
solutions that can preserve the sample. Samples also are dried by air – without
heat/sunlight.
Preservation is very important as it makes the evidence
intact and usable for DNA testing at a later stage.
Each item should be marked properly (on the container/envelope
or on large items)
Each item should be described precisely and entirely with
the corresponding case number with the date and time of collection mentioned.
Each specimen/item should be packaged in a separate
container, the container will be clean, and proper sized to prevent cross
contamination or damage.
Each packed item should be sealed to retain evidence and to prevent
from unauthorized handling.
Proper records should be maintained regarding each article/specimen
showing chain of custody, from the point of origin to its final disposition.
Every item should be photographed before it is collected as
evidence.
For seminal fluid it is necessary that they must be
collected before they lost or destroyed. Samples should be allowed to air dry
naturally or use a hair dryer on low speed. Wet samples must be drawn into an
eyedropper or pipette and should be placed in a sterile test tube. When found dry
stains on cloths, submit the entire article, remember not to break or
contaminate the stained area.
Blood and Bloodstains collection
Blood on absorbent objects should be dried in shadow and
air. All the materials should be packed separately. Large items packed in a
clean paper and small items in plastic phials.
Blood on non-absorbent objects –
If blood in large amount and wet then suck up liquid blood
with disposable pipette and then packed.
If blood present in small amount, rub cotton on the stain.
For large amount dry blood, scraped and used a scalpel to
transfer in to a hard plastic container.
For small amount dry blood, collect it by rubbing a piece of
moistened cotton on the strain.
Bloodstains on body collected by filter paper, cotton, or a
clean piece of cloth moistened with normal saline. After air drying, packed in
a paper envelope.
Pattern of bloodstains should be photographed (color) with
scale, collect the sample by swabbing stains with moist cotton and pack in a
paper envelop.
Saliva
Sample collected on white gauze, dry it and packed in a
plastic container.
Hairs and fibers
Hair and fiber evidence collected by plastic tweezers on a
paper, fold it and packed in a paper envelope or plastic bag. A separate comb should
be used for control sample from each area of the suspect body.
Skin with bullet hole
First take a color photograph of the hole, advised the
medical officer to cut the skin beyond the blacked area around the hole. Store
it in a glass jar containing 10% formalin solution.
Semen
Contamination is a key issue when it comes to preserving sperm
evidence, sample must be an isolated one and correctly identified and labelled.
Take color photograph, collect articles having it and allow air drying then
packed in paper bag or paper envelope.
Urine/Feces
Sometimes urine or feces left at the crime scene by the
offender. Urine can be collected by eyedropper or gauze and placed in a sterile
test tube or other container. If found on cloths then submit the entire
article.
For trace evidence you can use vacuum cleaner fitted with an
in-line canister, attachment in the hose, forceps or use tape. Forceps and tape
is the best method so as to not contaminate the evidence.
Fingernail scrapings obtained for an analysis of any blood,
skin or hair from the offender.
BIOLOGICAL EVIDENCE HAZARDS AND HANDLING
Remember that contact with bodily fluids can spread disease
(by blood borne pathogens) and
Persons handling biological evidence should take proper
safety.
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.