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Physical evidence
- any tangible article, small or large, which tends to prove or disprove a point in question. It may be used to:
- reconstruct a crime
- ID participants
- confirm or discredit an alibi
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In order for physical evidence to be introduces in a trial, an artical must:
- be properly ID'd
- show proper chain of custody
- be material and relevant
- meet all legal requirements
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Guidelines for proper collection and disposition of evidence
- ea. pc. of evid should be marked to show orig. position and location
- ea. article should be marked distinctively by the searching officer to ID the person who found it
- ea. item should be described exactly and completely with case numbers and date and time of collection
- ea. packg should be sealed ot retain evidence and prevent unauthorized handling
- ea. pc. of evid. should show proper disposition--police dept. lab, property clerk's office, FBI lab
- proper record should be kept regarding ea. pc. of evid. showing chain of custody
- ea. item should be photo'd before it's collected, to include long-range and close-range
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Evidence ordinarily falls within 3 distinct categories:
- body materials
- objects
- impressions
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Blood--Lrg Amounts/Pools
- use an eyedropper or hypodermic syringe to collect the fluid and transfer to a sterile container
- transfer immed. to lab or refrig specimen (DO NOT FREEZE)
- in some instances add sodium azide or EDTA to prevent spoilage
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Blood--Small Amts of wet
- use 100% cotton swab, #8 cotton thread, or gauze pad to collect specimen
- allow swab or gauze to air dry
- place in sterile test tube or other clean container
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Bloodstains Dry
- Nonporous surface--if sufficient amt., it can be scraped from surface with clean razor blade or sterile scalpel into sterile container
- Porous surface--collect and submit the article as found and wrap in separate and sterile container (if too big remove portion of item)
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Dry Bloodstains--Traces
- moisten a 100% cotton swab or gauze pad with distilled water (obtain control sample)
- stain will soften and soak into swab or gauze pad
- allow to air dry
- place into steril test tube or container for lab
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Next to blood, ________ is the physicological fluid most commonly discovered at homicide crime scenes.
Semen
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Semen--Wet Stain
- swab or wash
- draw fluid into an eyedropper or hypodermic syringe
- place in sterile test tube
- use swab or gauze pad for sampes of smaller quantities which are still moist
- allow to air dry and place in sterile container
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Semen--Dry Stain
- will have stiff "starchy" texture
- if on clothing, submit entire article
- on body, using gauze pad moistened with distilled water, gently remove stain and place in sterile test tube or container after allowing to air dry
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Urine
- remove by eyedropper or gauze pad
- place in sterile test tube or other container
- if on clothing, submit entire article
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Spittle or Saliva
- Remove with eye dropper or gauze pad
- Place in sterile test tube or other clean container after drying
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Feces--Lrg Amt
- remove with small clean shovel
- allow to air dry
- place in sterile container
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Feces--Small Amt
- remove with swab or gauze pad moistened with distilled water
- then air dry or scrape into container
- place in sterile test tube
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Vomit
- remove with eyedropper or small shovel depending on amt.
- place into sterile container
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Urine, saliva, feces, perspiration, ear wax, nasal mucus, etc. can be typed into the same grouping as blood from an individual who is a _________, approx. 80% of population
Secretor
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Tissue
- remove with tweezers
- place in a glass container or sterile test tube
- forward to med. examiner
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Hairs and/or fibers can:
- help determine the extent of crime scene
- place the perp at the scene
- connect the suspect to a weapon
- corroborate statements of witnesses
- determine the rout to and fro the scene
- be located in any number areas involved in the homicide (vic, scene, weapon, tool, vehicle, clothing, suspect)
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Determinations from Hair
- species
- race
- location of growth
- treatment
- how it was removed
- disease and or damage
- genetic info (blood type from shaft, other genetic markers and sex from pulled hair roots)
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It is recommended that a sample of hair from __________be obtained in all homicide cases
various parts of the body
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Sampling comprises approx _________ pcs. of hair. Hair removed from head should be taken from ____________. Then the roots should be ___________.
24-48; front, back, right, left, top; air dried
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Collection of Hair
- use oblique lighting
- gather by tweezers being careful not to bend or break
- masking or scotch tape can be used
- place in sterile container and seal (folded paper or envelopes can be used)
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Conclusions from Hair Samples
- did not come from unknown hair source
- could have come from known hair source
- sampling too limtd. for meaningful comparison
- no conclusion
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Bullet Collection
- bullets should be collected without damaging or marking the rifling
- bullets embedded in doors, trees, walls, etc. should be removed by taking out a portion of the object in which the bullet has become lodged rather than by probing or digging
- should be examined for blood or other materials before packaging
- should be marked on the base or nose
- ea. bullet should be packgd separately to prevent cross-contamination or accidental abrasion of rifling marks
- packg should be marked to show ID and location of discovery
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Discharged Cartridge Cases or Cartridges
- CC should be marked on the inside wall by the mouth end or as near to the opening as possible
- never mark CC on or near the end
- always consider the possibility of fingerprints on sides of CC and take appropriate measures to preserve them
- packg in separate containers with proper documentation
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Shotgun Shells
- plstc or paper should be handled in same way as other CC
- can be marked on metal side part of CC
- never mark on base of shot shell CC
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Live Cartridges
- examine for fingerprint evid prior to marking
- mark on side of cartridge
- packg, indicating the location of recovered rounds
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Shotgun Wadding
- Recover and submit
- place in separate container
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Weapons
- photo and examine for FP
- examine for any serology or other trace
- place in special container according to size
- forward to serology or crime lab for further analysis
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Firearms
- photo in orig position
- examine for FP
- examine for any serology
- unload and render safe before transporting
- packg individually in appropriate container (suspend by string thru trigger guard, or if long gun, lay weapon across container in notches at ea. end of the box)
- indicate finish, brand name, model designation, serial numbers, caliber, and number of shots the weapon is capable of firing
- mark for ID: revovlers--on frame, barrel and cylinder; rifles and shotugns--on receiver, bolt, and barrel; semiautomatic weapons--receiber, slide, barrel, and any clips
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Examination of Fibers will indicate origin as follows:
- vegetable--cotton and hemp
- animal--wool and mink
- mineral--glass wool and asbestos
- synthetic--nylon and orlon
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Examination of Fibers will determine if fiber is similar to the ______.
control sample
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Collect fibers as follows:
- forceps, tape (most practical), or vacuum sweeping (least desirable)
- place samples in individual containers from ea. area gathered, mark appropriately, forward to lab
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Fabric can be examined to determine:
- color
- type of cloth and fiber
- thread count
- direction of fiber twist
- dye
- (class and individ. characteristics can be obtained from frags of fabric by fitting the evid pcs into its source)
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Cig Butts
- collect with forceps or tweezers and insure dryness
- place into separate containers to prevent contamination
- containers should be marked appropriately
- forward to serology
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displaced furniture
- examine for FP and or serology
- useful in crime reconstruction
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soil
- color may be distinctive
- minerals can be distinctive
- baterial profiles can be distinctive
- vegetation can be distinctive
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tools
- examine for FP and serology
- may contain traces of certain materials that wer to be matched up with known samples
- portion of tool to be matched must be protected
- broken tools can be fracture matched for ID
- never try to fit tool into tool mark or match broken pcs.
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clothing
- stains on clothing may match stains from scene, vic, or suspect
- suspect's clothing may contain blood similar to the vic's
- vic's clothing may contain saliva and or seminal fluid from perp
- hairs or fibers may be present on clothing that match similar hairs or fibers from particular scene or location or from vic
- tears or cuts in clothing made by weapon can be matched to show position of vic at time of assault
- deposit of GSR on clothing can be analysed to determine the approx distance from which the gun was fired
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documents
- primary consideration in handling is preservation of FP
- collected by using tweezers or forceps
- ea. item should be placed in a sparate packg. (clear or see-thru is best)
- if see-thru packgs are not available, object can be photocopiedusing forceps to place the object on machine and back to envelope
- marking depends on type of examinations to be conducted
- should not be folded
- examine for LP
- saliva on envelopes can be blood-typed and somtimes analyzed for sex origin
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Latent Print Processing on Porous Materials
- 1st--iodine fuming--reacts with oil or fatty fluids
- 2nd--ninhydrin--reacts with amino acids in perpiration
- 3rd--silver nitrate--reacts to salt in perspiration when exposed to strong light
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Glass
refractive index proves that the known sample and the evidence may have come from similar source
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Glass can show __________ and ________ of bullet holes thru glass by examination of ________ and _______ fractures and may prove important in reconstructing the crime.
direction and sequence; radial and concentric
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Glass collection
- small pcs. should be place in vial or pill box
- larg. pcs. should be placed in sturdy cardboard box with proper padding/protection
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Latent print powders __________ interfere with serological analyses.
do NOT
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Ninhdrin sprays and other chemical means ______ interfere with serology tests.
may
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Plastic prints
impression occur when the finger touches or presses against soft pliable surface such as putty, gum, etc.
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Visible prints
occure when fingers, palms or feet which have been contaminated with foreign substance come into contact with clean surface and are pressed onto the surface leaving a print
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Latent print
occur from the natural skin secretions such as perspiration, when grease or dirt is mixed with it then a stable print may be deposited on the surface
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Powder processing
- a small amt of powder is poured onto a clean pc. of paper
- brush is drawn across the powder and then tapped with the finger to remove excess
- surface of object to be searched is then lightly brushed with curved strokes to locate prints
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Powder __________ to the ridge structure of the print, being careful not to rub the print too hard.
parallel
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The advantage of magnetic powder is that there is __________ left on the object.
no mess or excess powder
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Preservation of FP
on homicide scene, prints should be photo'd before attempting to lift them; use 1X1 fingerprint camera
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Chemical processes
iodine fuming, ninhydrin, and silver nitrate. further more, there have been some remarkable results in developing latent prints by use of the laser
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The __________ is the most common impression left at or near the scene of a crime.
footprint
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A _________ is formed when the foot or sole and heel of a shoe becomes contaminated with some foreign substance, such as blood, paint or dust. A ____________ is formed like a tire track, when the foot or tire treads are pressed into some type of moldable material such as dirt, clay or snow.
foot print; foot impression
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Collecting Impressions
- clean of foreign matter
- enhance with lighting
- scale
- photo
- cast--using 5 lbs plaster of paris, mixing container, stirring stick, reinforcement matrials, shelac or plastic spray, oil spray; clean out loose material, plastic spray to fix soil, build form, pour plaster, add reinforcement sticks
- collect soil sample
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Preserve dust prints
- photo 1st
- use special lifter placed sticky-side down over impression,
- press on lifter,
- and then remove lifter
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When the original tool mark can't be collected
- photo (long shot and 1x1)
- cast with silicone rubber after spraying surface with release agent
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Bite marks may be considered as ____ marks.
tool
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Bullet holes in wals/furniture
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Bullet holes in clothing
- photo
- safeguard for examination for GSR
- wrap (do not fold) and place in proper container
- direction can be ascertained with color (Harrison) test
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Newly damaged areas
- photo
- examine for any serology
- examine for any FP
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When unraveled, a molecule of DNA is approximately ____ in length
6 ft.
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Watson and Crick in 1953 determined DNA to be a ______ composed of pairs of purine and pyrimidine bases.
double helix
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DNA is made of nucleotides composed of
sugar, phosphate group, and a base
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Four bases are two (2) purines, ________ and __________, and two (2) pyrimidines, _________ and ____________.
adenine (A) and guanine (G) ; thymine (T) and cytosine (C)
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Adenine binds with __________; and Guanine binds with ___
Thymine; Cytosine
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The polymorphic junk DNA regions are known to repeat themselves over and over again like a stutter and are called ____________
Variable Number of Tandem Repeats (VNTRs)
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STR stands for _________.
Short Tandem Repeats
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Everyone uses ____________locus probes for DNA profiling
single
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In 1985, Kerry Mullis developed PCR or ____________________.
Polymerase Chain Reaction
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Three techniques are used by forensic scientists to extract DNA
- organic extraction,
- nonorganic extraction
- and the chelex extraction--only the chelex is unsuitable for use with the RFLP test
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RFLP Test
Restriction Fragment Length Polymorphisms
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