6 identification of blood, bloodstains, biological fluids and stains

what is SWGSTAIN and when was it formed?

scientific working group on bloodstain pattern analysis; was formed in 2002

what is an extracellular fluid + an example?

a fluid present outside of cells + blood is an example

what does plasma (the fluid portion of blood) contain?

cellular components such as red blood cells (RBCs), white blood cells (WBCs) and platelets

• The nuclei of WBCs contain the source of DNA for blood

When blood clots, the liquid portion that doesn’t clot is known as what?

serum

what do the nuclei of WBCs contain? 

blood

what must happen to create a blood splatter?

an external force must take over the surface tension

• surface tension is the force that pulls the surface molecules of a liquid to its interior

  • This decreases its surface area and causes it to resist penetration

the weight of a substance relative to the weight of an equal volume of water is known as what?

specific gravity

Blood drops falling will increase in speed until the drag force equals the gravitational pull. What is this known as?

terminal velocity

• Falling blood at increasing heights will also produce increasing diameters of bloodstains, but heights higher than 7 feet will not increase

how does the geometry of bloodstains help determine the direction?

• examine the edge characteristics of individual stains

• the narrow end of an elongated bloodstain usually points in the direction of travel

• determine the directionality of multiple bloodstains

• draw a straight line through the long axes of the bloodstains to determine the area of convergence

what angle does blood have to strike at for it to be circular or elliptical?

it has to be 90 for it to be circular, otherwise elliptical

• connecting elastic strings at the base of each bloodstain and projecting them up from the two-dimensional area of convergence

this is known as what?

stringing

Impact spatter associated with gunshots may produce spatter smaller than 0.1mm in diameter, known as what?

Misting

• is associated mostly with gunshots, but can also be caused by explosions, high-speed machinery and high-speed automobile collisions

two sources of misting when associated with gunshots?

• Back spatter fires back at the source/shooter

• Forward spatter is projected forward in the same direction that the bullet was shot from

  • Generally has more blood

what is the size range for impact spatter associated with beating and stabbing

generally 1-3 mm in diameter

• Exposed blood must exist for spatter to start happening, but the bloodied area itself doesn’t have to have an impact

• Size range of spatters from different mechanisms can be similar, so it’s not always possible to determine it

Single drops of blood will produce small spatters around the parent stain (as a result of striking the ground at impact), known as what?

Satellite splatter'

• Multiple factors can influence blood splatter, including freshness of the blood, blood drop volume, surface texture and distance

Subsequent blows to the same general area where a wound and blood have occurred produce what type of pattern?

Cast-off

when do splashed bloodstain patterns occur?

When a quantity of blood more than 1 ml is subjected to minor force/drips onto a surface

• Large central areas with peripheral splatters

• Secondary blood splashing or ricochet may occur

when do projected bloodstains occur?

when blood is projected, exceeding the force of gravity

difference between splashed and projected bloodstains?

splash patterns are driven by gravity, and projected patterns are ejected with a stronger force (ex. Arterial spurt)

when do transfer bloodstain patterns happen?

when an object wet with blood comes into contact with a secondary surface

• Sometimes a mirror image of the object is produced, which can help in determining it (e.g. knife, shoe, etc)

• Partial bloody impressions are often chemically enhanced to see more detail

what is a skeletonized bloodstain?

• when the center of a dried bloodstain flakes away and leaves a rim

what time period for clotting is normal in healthy individuals? 

3-15 mins

what three things can all alter bloodstains?

heat, soot and fire

what are void areas?

The omission of bloodstains in continuous patterns of staining

• Usually due to items that have been moved that were splattered with blood

what two questions arise when analyzing bloodied garments?

• Who’s blood is it?

  • DNA technology can determine this

• How was the blood deposited on the garment?

  • Bloodstain pattern analysts can determine how it was deposited

two categories of depositing blood on garments?

passive (dripping, transfer, flow, etc) and active (impact spatter, arterial spurts/expirated blood, castoff) bloodstaining

• the examination and analysis of bodily fluids in a legal context (blood, saliva, semen, urine)

This is known as what?

Forensic serology

• Very often, samples and stains are deteriorated, making analysis harder

• DNA analysis is much more powerful and discriminatory than serology

how is absence of evidence not evidence of absence?

• In many cases, blood originating from the victim that’s found on the suspect is powerful individual-characteristic evidence

• But, the absence of blood splatter on a suspect does not mean they weren’t involved in the bloodshed

• It’s not uncommon for an assailant to have little, if any, blood on them after committing a crime

  • May have changed clothes

cellular components make up for what percent of blood?

45%

• WBCs (transports oxygen and bicarbonate)

• RBCs (active in fighting diseases)

• Platelets (for clot formation)

DNA typing targets nucleic data, therefore requiring WBCs

the noncellular component, plasma, makes up for what percent of blood?

55%

• Serum (carries protein and electrolytes)

• Fibrogen (material that forms clots)

the identification of blood contains what?

a presumptive test that is followed by a confirmatory test

• There’s not one test specific for blood

• Presumptive tests can include colour change reactions or release of light

what are false positive and false negative results in blood tests?

False positive results (a positive result with a substance other than blood) and false negative results (a negative result even when blood is present) are inevitable with presumptive tests

• False negative results can happen with the presence of chemical oxidants that aren’t from blood

how do catalytic colour tests work?

• Uses chemical oxidation of a chromogenic substance (one that changes colour with a reaction) with an oxidizing agent that is prompted by the presence of blood, specifically hemoglobin

  • Solution of the chromogen is added to the suspected bloody sample

  • An oxidizing agent is added after

  • A rapid colour change constitutes a positive test

what reaction does benzidine (alter test) result in?

• a characteristic blue to dark blue colour

• Seldom used now

explain tetramethylbenzidine and hemastix?

• Derived from benzidine

• Reaction results in a colour of green to blue-green

• The chemical reaction has been made portable with the use of Hemastix for convenience and safety at crime scenes

explain Phenolphthalein (Kastle-Meyer Test)?

• Commonly used in forensic labs, and is an acid-base indicator

• Produces a bright-pink colour

• The reagent consists of reduced phenolphthalein in an alkaline solution which is later oxidized by peroxide in the presence of hemoglobin

explain the process of tests using chemiluminescence and fluorescence?

spraying a chemical mixture onto suspected areas in the dark, with the aid of an ALS (alternative light source)

• Light is produced from the reaction of luminol with blood, which helps observe more detail

• These tests can have potential for contamination

• Luminol relies on chemiluminescence, the process of light being emitted from a chemical reaction (the most sensitive presumptive test)

• Fluorescin relies on fluorescence which happens when light is emitted after absorbing light energy (ex. UV)

what do luminol and fluorescin rely on?

• Luminol relies on chemiluminescence, the process of light being emitted from a chemical reaction (the most sensitive presumptive test)

• Fluorescin relies on fluorescence which happens when light is emitted after absorbing light energy (ex. UV)

what are crystal tests + two types?

Crystal tests are a type of confirmatory test, they target the non-protein heme group of hemoglobin, where crystals are microscopically observed

• Two types are the Teichmann and Takayama tests

when are confirmatory tests for blood done?

after positive presumptive testing

• May go straight to DNA testing as only human DNA is detected in this method

determining species origin in bloodstains?

• Based on immunological reactions where an antigen (Ag) reacts with an antibody (Ab) to produce a precipitate (solid) as a positive result

• Antibodies are found in the serum of human blood

• Not as common, as dna typing is human specific

what did genetic marker systems do?

characterized blood prior to DNA typing

what is the ABO grouping system?

• Types A, B, O, and AB refer to the antigens present on RBC’s with corresponding antibodies present in the Plasma

• Forensic testing using this system identifies both the antigens and antibodies on a bloodstain or person

explain enzyme markers?

• Also used before DNA testing was more popular

• Enzyme systems identified different types of enzymes

  • Allowed for a greater ability to discriminate between individuals compared to ABO grouping

• Many methods have been developed

second most common fluid in forensics beside blood?

semen

spermatozoa and azoospermia?

sperm cells, while azoospermia is semen without it

common method of detecting semen?

staining the sperm cells for visualization under a microscope

• Characterization of enzymes is used to identify semen

• Identification of spermatozoa (prostate-specific antigen, PSA) is the generally accepted confirmatory test for semen

what are acid phosphates?

a class of enzymes that catalyze (push forward) the hydrolysis of certain organic phosphates

• No correlation between the level of SAP and amount of sperm cells

what is saliva?

Slightly alkaline solution of water, mucus, proteins, salts and enzymes found in the mouth to help with digestion

• No specific test for saliva, but it traditionally relied on detection of alpha-amylase enzymes

  • Found in many body fluids, but at levels 50x higher in saliva

explain urine testing?

• Performed less frequently due to the tests being insensitive and low success rate with DNA profiling

• Detection relies on identifying two compounds:

  • Urea

  • Creatinine

• Urease breaks down urea into ammonia and carbon dioxide, and ammonia can be detected using an indicator chemical

how are vaginal secretions detected?

• Identified on the basis of detecting glycogenated epithelial cells, using a PAS (period-acid Schiff) reagent that stains the glycogen bright magenta

  • Not a conclusive test

  • The amount of glycogenation depends on the stage of menstrual cycle, and they are absent from pre-pubescent females, as well as being uncommon in postmenopausal women

• The test is also destructive to the sample, impeding the available amount of DNA for profiling