DNA Evidence

BIOLOGICAL/­ DNA EVIDENCE

     

Biological/­D NA Evidence

Evidence impact Biological evidence is strong evidence when exploitable DNA is available. Human DNA is found in body fluids (blood, semen, saliva, sweat) as well as in other biological cell material of tissue, hair (root), teeth, or bones. It allows: • identification of person (suspect, victim) • reconstruction (activities, incident sequence) • forensic intelligence (serial crime, DNA database) Biological evidence is mostly latent evidence and extremely exposed to contamination. Strict use of personal protective equipment is mandatory whenever assessing biological evidence.

Evidence assessment General situation •  Any zone of contact to leave biological evidence (objects, persons) • Visible body fluid stains (blood, semen)

Search for latent biological evidence • Latent body fluid stains: search with alternative light source

Standard procedure for all contact evidence • Photograph visible or presumed (latent) evidence 113

TYPES OF EVIDENCE

• Whenever possible collect item and submit, especially for absorbent carrier substrate (fabrics, paper), eventually cut out • Or: swab

Stains of blood/semen/saliva • Photograph • Liquid: absorb with swab • Person: swab (sexual assault: ask for medical assistance) • Dried on object: collect item or swab • Blood spatter sketch and measure or use 3D laser scanner (blood pattern analysis!)

Fingernails • Photograph • Cut off or swab

Tissue/human remains/urine/feces/liquids • Photograph • Preserve all or sample (pipette liquid sample) • Freeze

Bite marks • Photograph (use ruler!) • Collect item or swab

Hair • See Part III – Hair evidence 114

Biological/­D NA Evidence

Use of presumptive tests for blood/semen, chemical enhancement •  Consider limitations and risks (sequence, contamination) • Ask for specialists’ support •  Photograph result (color reaction, enhanced stains)

Collection of comparison sample • Blood: ask for medical assistance • Buccal swabs: use DNA-free swabs

Protect and preserve • Against any DNA contamination • Strictly use personal protective equipment • Against heat (direct sunlight) and humidity— consider storage conditions

Time factors •  Not properly packaged biological evidence might result in contamination or destruction of DNA—submit as soon as possible •  DNA evidence may be compromised by exposure to UV light (sunlight, forensic light source) • DNA evidence may be compromised by water (dilution) 115

TYPES OF EVIDENCE

• Human tissue, urine, feces, foodstuffs: store in cool place or freeze as quickly as possible • Bite mark pattern: will modify quickly shape and color—record and swab

Document • All visible stains—eventually sketch or use 3D laser scanner (blood-pattern analysis) • All zones of assessed latent evidence • All other biological evidence (fingernails, tissues, bones, teeth)

Take notes • All evidence assessment activities • Eventual cross-contamination • Zone of assessment, eventually sketch • Use of presumptive tests and chemicals • Collection of reference samples

Package carefully • Separately • Seal and label DNA •  Wet/humid items: dry before packaging (stained fabrics) • Liquid samples (urine, feces, blood in water/ snow: tight glass containers) 116

Biological/­D NA Evidence

Attention Do’s • Consider sequence of recovery of any other evidence type • Change gloves frequently

Don’ts • Use adhesive tapes to collect DNA evidence • Use airtight plastic container for solid evidence, but paper bag/cardboard box (risk of rot!) •  Scrape off dried body fluid stains (blood, semen)—collect item

Necessary tools • Alternative light source • Biological/DNA evidence kit (swab kit, sexual assault kit) • Measurement kit • 3D laser scanner

Check for more evidence information Part I • Break and entry: Volume crime evidence • Explosion and arson: Safety risk evidence • Fraud and forgery: Document evidence 117

TYPES OF EVIDENCE

• Hit and run: Automobile accident evidence • Homicide and rape: Violent crime evidence • IT and multimedia: Digital evidence

Part II • Documents • Fabrics • Firearms • IT • Unknown substances • Vehicles

Part III • Biological/DNA evidence • Bullet and cartridge evidence • Explosive debris evidence • Fiber evidence • Fingerprint evidence • Fire debris evidence • Footwear and tire mark evidence • Glass evidence • Gunshot residues (GSR) evidence • Hair evidence • Paint evidence • Soil and plant evidence • Toolmark evidence

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