Forensic Science Definition w Forensic Science is the
- Slides: 38
Forensic Science Definition w Forensic Science is the application of science to those criminal and civil laws that are enforced by police in a criminal justice system. w Criminalistics – services provided by a crime laboratory
Sherlock Holmes w First novel in 1887 w Written by Sir Arthur Conan Doyle w Sherlock Holmes - Forensic Scientist? w Used serology (blood analysis), fingerprints, firearm examination, document examination before it was used by real life criminal investigators
Forensic Laboratories w FBI Lab - Largest in the world w Established in 1932 w Over 1 million examinations per year w FBI Crime Lab w RCMP labs – 6 sites w RCMP Forensics n Do DNA, trace evidence, counterfeit and document examination, explosives, firearms and toxicology
Problems with New Technology w OJ Simpson: 1994/95 w DNA evidence used w Acquitted, then convicted in civil case
The Crime Scene w Several Phases to Crime Scene Investigation n n n Security Recording Search Collection Chain of Custody Controls
Securing the Crime Scene w The first on the scene is usually the police w The first priority is to to check bodies for signs of life, close off the site (with ropes or tape), and to call appropriate services (eg. Ambulance, Medical Examiner) w Path of entry and/or exit may be established
Recording the Scene w Important to record scene before it is disturbed in any way w Regular (not digital) photography is still the ‘gold standard’ because they are difficult to alter w Videotaping also is often done w Sketches, and notes can be important additions as the evidence may not be used for months w Some tape a narrative and then transcribe
Photography w Must be done from differing angles w Close-ups of body, weapons, blood stains, etc. w Also overview photos of scene, body and surface under body after it is removed
Sketches w Often done because investigators must quickly begin processing the scene w CAD programs now help investigators do accurate sketches for court proceedings w Any notes taken should include who discovered any evidence, the time discovered, and the place of discovery
Searching for Evidence w w w Head investigator decides what area to search Can be very time consuming and tedious Visual searches often done over large areas ‘Fingertip Searches’ can be done over smaller areas Screens sometimes used to find small evidence in soil, etc. w Grids often made to ensure complete coverage
Vehicle Searches w Vehicle searches are often done at a police garage – entire car is often vacuumed and dust is collected analysed w Undercarriage of car is also searched (soil, pollen, vegetation, etc. )
Collecting Evidence w Investigators carry several types of collecting containers (plastic bags, vials, envelopes, etc) w Each sample must go into a separate container to prevent contamination w Evidence (eg. hair, etc. ) from smaller items is not removed – entire article taken to lab w Evidence on larger structures (eg. Floor, wall) can be removed with forceps, scraped or swabbed or the piece may be cut from building (eg. Wall) w Gloves should be worn to prevent DNA and other contamination of samples
Chain of Custody w Every person that handled or examined evidence must be accounted for w Every transfer of custody of evidence must be documented (to prevent accusations of tampering) w Transfers are thus kept to a minimum w Body needs chain of custody as well
Controls w For comparison, the investigator must, if possible, obtain samples to compare the evidence to w For example, paint from suspect vehicle to compare to paint at the scene, blood samples from suspects, soil from suspect’s yard
Crime Scene Safety w Infectious diseases (AIDS, hepatitis) in tissue and blood samples (double gloves, Tyvek shoe covers), possibly liquid repellant suits w Particle mask, goggles, or face shield when applying aerosol chemicals or scraping blood w Sharps – removed and labelled as soon as practical
Crime Scene Safety w Potentially infectious materials used (eg. Swabs, masks, pencils) should be disposed of in a ‘biohazard’ bag and taken for incineration w No eating, drinking or smoking
The Body – Time of Death w First measurement is often the time of death w Internal body temperature taken w 1. 5 – 2 degrees F per hour for the first 12 hours (normal is 98. 6) w For the next 12 hours, temperature decreases at half this rate w Temperature of surroundings, water can alter these calculations substantially w Clothing on body may also alter estimate
The Body w Rigor mortis – the term used to describe the stiffening of the muscles that occurs after death w Begins about 2 hrs after death w Begins with the eyelids and spreads to muscles of face and jaw, then arms, trunk and finally legs
The Body w For 12 – 48 hours, the body remains stiff w After 48 hrs, decompostion begins body begins to ‘relax’. w Also an eyelids to legs progression
The Body w ‘cadaveric spasm’ is sometimes confused with rigor mortis w This is a muscular contraction that occurs immediately at death w This condition relaxes in hours, enabling any object grasped to be removed
The Body w w “livor mortis’ – is the ‘bruising of death’ Red blood cells descend to the ‘bottom’ of the body About 2 hours after death ‘lividity’ can be seen CO poisoning (bright red) and cyanide poisoning (bright pink) can cause colors other than regular purple color
The Body w Eyeball sampling is a new technique for determining time of death w As red cells break down, they release potassium ions w This diffused into the vitreous humor of eye w This diffusion occurs at a slow but constant rate – quite accurate
The Body w If the time of death is longer than 48 hours, the date of death can often be determined w The decay process follows a predictable pattern w Bacterial breakdown of blood causes a green staining of flanks of abdomen after 2 days w This spreads to arms, legs and neck in a day or two w Body begins to swell (gaseous products of decompostion) w Blisters form on skin in a week
The Body w If outdoors, insect life cycles are often used to estimate date of death w Blue bottle and green bottle flies, houseflies, and blowflies are often the first to colonize bodies w Lay eggs on fresh flesh only w Eggs hatch 8 – 14 hours later (temperature dependant) w Maggots go through 3 stages – shed skin each time
The Body w Fully grown flies emerge 10 – 12 days after eggs are laid – fly away w Coffin flies – expose bones w Fungus grows on bones w Woodlice graze on fungus w Body farms – are often used to estimate rates of insect development
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