COLLECTION AND PRESERVATIONOF FORENSIC SAMPLE

Aim :Sample is collected to conduct the forensic examination in order to prove or disprove whether there is a link between individual(s) & the objects and the place of evidence .

Forensic specimen collection techniques :

When collecting specimens for forensic analysis, the following principles should be strictly adhered to:

Avoid contamination: Ensure that specimens are not contaminated by other materials. Wear gloves at all times. Modern DNA assay systems are very sensitive and may detect small amounts of extraneous material.

Collect early: Try to collect forensic specimens as soon as possible.The likelihood of collecting evidentiary material decreases with the passing of time. Ideally, specimens should be collected within 24 hours of the assault; after 72 hours, yields are reduced considerably

Handle appropriately: Ensure that specimens are packed, stored and transported correctly.

As a general rule, fluids should be refrigerated; anything else should be kept dry.

Label accurately: All specimens must be clearly labeled with the patient’s name and date of birth, the type of specimen, and the date and time of collection.

Ensure security: Specimens should be packed to ensure that they are secure and tamper proof. Only authorized people should be entrusted with specimens.

Maintain continuity: Once a specimen has been collected, its subsequent handling should be recorded.

Details of the transfer of the specimen between individuals should also be recorded.

It is advisable to check with local authorities regarding the protocols for the recording of such information.

Document collection: It is good practice to compile an itemized list in the patient’s medical notes or reports of all specimens collected and details of when, and to whom, they were transferred.

Requirements : Common requirements are:

handglooves,sterile swabs,sterilewater, syringes,scalpel or blade ,foreceps ,plastic wares,brownpaper, EDTA tubes,zip lock polyboxes,glass slides,preservates,tubes, lifting tape, clipper Pen/board marker

cotton guage etc.

Common biological samples encountered:

Whole fresh blood.Blood stain( dry).Seminal stain.Hard tissue(bones).Soft tissue (body organs).Hair.

Buccal sampleSkin.Finger nails.Methods of collection:Whole blood sample: sterile needle

should be used while collecting blood and put in EDTA vial.if blood is pooling then collect on sterile cotton or gauze pad.

Blood stain: should be picked up on sterile cotton guage using sterile foreceps and blade.

If blood stain is,On clothing,if possible,wrap the item in

clean paper,place the article in a brown paper bag or box and seal & label container.

On small solid objects,send the whole stained object to the lab,after labelling and packaging.

On large solid objects:It is usually impractical to deliver the whole object to the Laboratory, scrape the stain onto a clean piece of paper, which can be folded and placed in an envelope. Seal and mark the envelope.

. Do not mix dried stains. Place each stain in a separate envelope.

. Never attempt to wipe dried stains from an object using a moistened cloth or paper.

. Dried blood stain can also be collected by using lifting tape :

For dried blood stains on a non-absorbent surface, fingerprint lifting tape may be placed over the stain and lifted off.

The stain is transferred to the adhesive side of the tape, which may then be secured on a clear piece of acetate for submission to the laboratory.

Seminal stain: Should not be touched by hand especially the stain portion. Should be picked up with sterile forceps.

Hard Tissues( Bones): Bones should be picked up using gloves, Kept at a place where there are no chances of environmental contamination. It should be allowed to dry completely.

Soft Tissues: Body organs should be collected using forces and wearing gloves. these should be kept in a sterile container.

Hair: Hair roots are preferred for the analysis. Hair roots should be picked up using sterile forceps.

Buccul sample: should be collected by using dry sterile swab in whole mouth between cheeks and gums,on and under tongue, in dentile fissures.

Skin: drip 3-4 drops of sterile water on swab & roll it on body with moderate pressure and immediately roll another dry swab on same area.

Fingernails: analysis for recovery of body fluids/DNA/other materials or comparison with broken fingernails at the scene.

Clip the fingernail of one hand at the time, over paper or drape & pack separately in addition to this swab under nails ,on surface of nail and around cuticle.

Table :DNA content of biological samples

TYPE OF SAMPLE AMOUNT OF DNA

liquid blood 20000-40000 ng/ml

bloodstain 250-500 ng/cm2

liquid semen 150000-300000 ng/ml

hair with root 1-10 ng/root

liquid saliva 1000-10000 ng/ml

oral swab 100-1500 ng/swab

bone 3-10 ng/mg

tissue 50-500 ng/mg

Precautions for sample collection: Wear gloves. Change them often. Use disposable instruments or clean them

thoroughly before and after handling each sample.

Avoid touching the area where you believe DNA may exist.

Avoid talking, sneezing, and coughing over evidence.

Avoid touching your face, nose, and mouth when collecting and packaging evidence.

Air-dry evidence thoroughly before packaging. Put evidence into new paper bags or envelopes,

not into plastic bags. Do not use staples.

Package all biological evidence in paper bags or envelopes (do not use plastic).

The packaging of biological evidence in plastic or airtight containers must always be avoided, because the accumulation of residual moisture could contribute to the growth of DNA-destroying bacteria and fungi.

Preservation

Whole Blood: Blood should be collected in sterile container containing an anticoagulant. The mostly preferred is EDTA.

It should be mixed properly but gently for some time. The container should be covered with parafilm to avoid slippage.

Should be kept it at 40C or using ice during transportation till it reaches laboratory for analysis

Blood stain: Blood stain should be dried properly. In semi dry stain there, is a possibility of bacterial growth thus chances of having contamination.

After complete drying it should be wrapped in a fresh blotting paper and packed in a  Zip lock poly bag.

No preservative is required. It can be transported at environmental temperature.

Seminal stain: Likewise seminal stain should also be dried properly. In semi dry stain there, is a possibility of bacterial growth thus chances of having contamination.

After drying it should be wrapped in a fresh blotting paper and packed in a Zip lock poly bag.

No preservative is required. It can be transported at environmental temperature.

Hard Tissue: No preservative is required. The hard tissues should be wrapped in the blotting paper and placed in a zip lock poly bag.

Soft tissue: It should be placed at 40C or in Ice till it reaches laboratory for analysis.

Hair: Hair roots should be placed in a blotting paper and then packed in a zip lock poly bag. It requires no preservative and can be transported at environmental temperature.

Buccul sample: should be collected on sterile swab and swab should be placed in tube. storage can be done by freezing.

Skin: sample collected by swab should be placed in tube and then in tamper- evident bag. Storage by freezing.

Fingernails:collected by clipping on paper should be packed in zip lock poly bag/tamper evident bag along with clipper , swabs used should be placed in tube and store by freezing.

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