Forensic Science Exam 2

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Serology and characteristics

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Study of antibody antigen reaction. Inexpensive and easy, good for preliminary testing, field testing, sensitive but not definitive.

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Forensic science serology

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Study of blood serum, along with saliva, semen and other bodily fluids in relation to crimes and other legal matters

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Antibody

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Immunoglobal/protein that recognizes a foreign muscle/antigen. Produced by B lymphocytes

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Polyclonal

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A mixture of antibodies that are produced by different clones of B cells and bind to different antigen sites.

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Monoclonal antibodies

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Produced by the same clone B cells and bind to the same antigen sites.

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Antibody for diagnostic use

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Small, water soluble, stable, easy to conjugate

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Sensitivity

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80 ÷ (80 + 20) x 100%= 80%. Neg result suggests absence of substance/disease. False neg unlikely, but can have false positive. Screening/presumptive tests: high sensitivity most useful.

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Specificity

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900 ÷ (900 + 100) x 100%= 90%. Pos result means high probability of presence of substance/disease. False pos unlikely. Confirmatory tests: high specificity most useful, and only for substance in question.

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Blood

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Cells suspended in a matrix. RBC, WBC, platelets, plasma.

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Plasma

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90% water, 10%: proteins, antibodies, lipids, carbs, salts, minerals, enzymes

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Serum

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Liquid remaining from plasma after blood has clotted, platelets and clotting factors form clot. Used in lab tests.

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Blood groups and types

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300 blood antigens, 30 blood groups. Types A, B, AB, and O.

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Blood group forensics used in

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Paternity testing, exclude paternity, maternity, baby mix-ups. Alleged perpetrators, exclude innocent, crime victims, clarify blood source.

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Phenolphthalein method in serology

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Most common, very sensitive on diluted blood, old blood, but crossreacts with other substances. Doesn't destroy DNA. moisten cotton swap with distilled water, wipe across stain, add colorless phenolphthalein, add drop of hydrogen peroxide, pos will be pink.

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Luminol method

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Reacts with hemoglobin, emits blue-white to green-yellow, sensitive, temporary - about 30 seconds, false pos. Mix with oxidant, and water, spray on area, observe in dark or with special light, photo within 30sec, may affect other tests.

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Fluorescein

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For vertical surfaces, fluorescence, use alt light source, may interfere with later tests, DNA analysis ok.

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Human or animal blood

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Only humans have antibody. Pass sample of antibody and antigen through gel. Hematrace card replacing ouchterlony

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Semen testing

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In post puberty males, made of cells, amino acids, enzymes, sugars, salts.

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Presumptive semen tests

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Brentamine fast blue B: reacts to acid phosphatase, moisten cotton swap with sterile water, apply to stain, add reagent. Pos = intense purple within 1-2 mins. Semen = strong pos. Vaginal and other bio fluid = weak.

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Semen flourences

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Black light, fast/easy, urine and saliva also show up.

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Microscopic semen examination

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Presence is conclusive. Absence is not conclusive.

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Sperm survival

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Vagina: three hours

Cervix: several days

Rectum: 6-65 hours or next bowel movement

Level of P30 shows time elapsed

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Salvia can be retrieved from

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Bite marks, licked adhesive, eating/drinking surfaces, spitting.

Contains skin cells, used for DNA testing, hard to see, test for amylase (high in saliva, but also found in other bodily fluids)

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Urine testing

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Use urease, contains few skin cells, DNA testing not useful.

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Human leukocyte antigen

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Expressed on WBC, more complex than ABO. Premier serological tool of 1960s and 1980s, used in paternity and personal ID

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Forensic entomology

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Study and use of arthropods as evidence in legal investigations.

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Forensic entomology divided into

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Medico-legal, urban, stored products.

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Urban entomology

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Majority of legal cases. Insects that affect human areas. Cockroaches, ants, flies, other vermin, stinging insects, termites, bed bugs

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Stored products entomology

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Second largest number of legal cases related to food contamination. Government food tolerances.

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Medico legal entomology

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Necrophagous arthropods (insects that feed on decaying flesh) often used to estimate PMI

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First insects on scene: Calliphoridae/blow flies

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Within hours

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Second insects on scene: muscid/house flies

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Within hours/days depending on wounds

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Third insects on scene: Piophilid/cheese skippers

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Upon putrification

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Fourth insects on scene: Staphylinid, hister, solid beetles (not normally used, often maggot predators)

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Fourth on scene

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Last insects on scene: dermestids

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Feed on hide and hair

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Entomology crime scene protocol

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Close coordination with other CSI, collect insects in, under, around body, and in soil, collect flying insects, document, CoC.

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Insects handling and preservation

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Label all on site, flying insects (DNA sampling when preserved), preserve all in ethanol.

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CODIS sample entries

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Crime scene, convicted offenders, arrestees, suspects, missing persons, unidentified human remains.

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CODIS hierarchy

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NDIS (admin), SDIS (databasing DNA analysis), LDIS (casework DNA analysis)

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CODIS

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Goal to link crime scene DNA profiles between serial crimes, and ID new persons of interests. Communication between LEA, driven by computer tech.

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CODIS kinds of samples

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Blood is more reliable, but oral is easier

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Manipulation blank control

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No contamination

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Amplification pos control

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Complete amp

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Amplification neg control

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No contamination

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Internal size standard control

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What size are the peaks

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Allelic ladder

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Number of repeats at that particular size

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Twins

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Identical DNA, but different fingerprints

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Chimera

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A mosaic of DNA profiles in a single person

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CODIS entry and search

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Complete profiles, searched against state and national, info released for exact matches.

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CODIS release and follow up

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Released to LEA, new sample requested from the match

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Bloodstain pattern analysis

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To confirm or refute assumptions concerning events and their sequence

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Blood stain patterns may reveal

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Origins of blood, direction from which blood came from, speed from source, position of victim and assailant, movement of victim and assailant, number of impacts

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Physical properties of blood

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Viscosity, surface tension, specific gravity, volume

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Blood surface tension

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Resistance to penetration and separation. Surface acts to to reduce surface area.

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Dripping blood

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Accumulates until weight > surface tension. Single drop breaks off. Settles into 0.05mL

And doesn't break until impact.

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Drop size and shape factors

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Standard = 0.05mL

Shaking/movement = smaller drops

Rapid bleeding = bigger drops

Depends mostly on nature of target surface

Texture (rough/smooth)

Porous/non-porous

Distance fallen

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Blood Distance fallen vs size

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No change in diameter beyond 7ft

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Blood spatter velocity

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Low velocity = 5ft/sec, 1.5m/s free falling/cast off/dripping/splashing/arterial spurting

Med velocity = 25-100ft/sec, 7.5-30m/s baseball bat blow

High velocity = >100ft/sec, 30m/s gunshot, machinery

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Blood spatter factors

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Tail points direction of travel and away from origin. Drop selected should be good size, complete shape, have a tail.

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Blood drop measurements for calculations

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Measure greatest width and length excluding tail

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Point of convergence

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Found by drawing lines through long axis of blood drops, circle intersection, and measure. 2D point of where person was standing. The more oval the further away.

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Area of origin

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Found by multiplying ADJ or AOC distance by the Tan of the angle. 3D point in space.

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Blood spatter calculation result

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Doesn't give finite point, just an area. 10% accepted error rate