Identification of Blood, Bloodstains, Biological Fluids, and Stains (Chapter Eight)

Red Blood Cells

• Carry oxygen and carbon dioxide (and other respiratory gases) to all parts of the body

• Contains hemoglobin

  • Protein that contains iron that binds to oxygen

  • Responsible for the red color of blood

White Blood Cells

• Fights disease and foreign elements

• Only blood component to have nuclei

Platelets

Aid in blood clotting and repairing damaged blood vessels

Plasma

Contains antibodies, hormones, clotting factors, glucose, amino acids, salts, minerals

What Determines A Person’s Blood Type?

Their red blood cells

Type A Blood Types Have Which Antigen?

Antigen A only

Type B Blood Types Have Which Antigen?

Antigen B only

Type AB Blood Types Have Which Antigen?

Both Antigen A and Antigen B

Type O Blood Types Have Which Antigen?

Neither Antigen A or Antigen B

If A Person Was Given Antibodies That Bind To Antigen A, And The Blood Clumps, What Does That Mean?

• The person’s blood contains Antigen A

• They can have either Type A or Type AB blood

If A Person Was Given Antibodies That Bind To Antigen A, And The Blood Does Not Clump, What Does That Mean?

• The person’s blood does not contain Antigen A

• They can have either Type B or Type O blood

Falling Blood Droplets Are In A Perfectly _____________ Shape Unless Other Forces Are Acting Upon It

Spherical

The Cohesiveness Of Blood Causes

• A perfectly spherical shape (while falling from gravity) unless other forces act upon it

• Has a dome shape when it strikes a surface and flattens out

The Adhesiveness Of Blood Causes

Spines that are connected to the main blood drop when blood hits a porous surface

The Pointed End Of A Blood Splatter Indicates

Direction of travel (moving away from impact)

Fine-Mist Spatter Pattern

• Less than 1 mm

• Produced by a high-velocity impact (gunshot)

  • Misting is typical of gunshot wounds, not seen in many other instances

Beatings or Stabbings

• 1-4 mm

• Produced by a medium-velocity impact

Beating with a blunt object, passive blood dripping

• 4-6

• Produced by a low-velocity impact

Area Of Convergence

• 2D area in which blood stain originated (does not show height)

• Draw straight lines opposite the direction of travel and draw a circle where all lines intersect

As The Angle Of Impact Decreases From 90 to 10, The Bloodstain’s Shape Becomes More ________________

Elliptical

Area Of Origin

• 3D area in which blood stains originated

• Found by examining the angle of impact and the area of convergence

Ratio For Discovering Angle Of Impact

Width/Length of blood splatter

How To Find Angle Of Impact

Take the inverse sine (arcsine) of the ratio (width/length)

Castoff Pattern

• These stains are typically linear and large

  • Blood is thrown from a weapon used in a beating

Transfer Pattern

• Wet blood contacts a second surface

• Leaves a pattern

  • Bloody shoeprint

Wipe (Pattern)

• A dry object moves through pre-existing blood with a lateral motion

• Feathered ends indicate direction of wipe

  • Bloody swipe of fingerprints

Swipe (Pattern)

• Lateral transfer of wet blood from a moving source onto a surface

• Feathered edge indicates direction of transfer from source

  • Bloody hair dragged across floor (Thick Swipe)

Arterial Gush (Pattern)

• Blood exiting under pressure from an artery and striking a surface

• Peaks indicate heart contraction

• Peaks get progressively smaller with blood loss

  • Sporadically dotted peaks

Expirated Blood (Pattern)

• Mist/spatter of blood due to blood being blown out of nose or mouth

• May contain mucous or air bubbles

  • Air bubbles are a decent indication of expirated blood

  • Blood blown out of nose or mouth as a result of air pressure

    • Similar to high velocity blood spatters

  • Blotches of blood everywhere

Shadowing Or Void (Pattern)

• Area with no blood on it while surrounded by blood

• Indicates that an object has been moved

Precipitin Test

Distinguishes between human and animal blood

Benzidine Test

• A regent once widely used as a presumptive test (possibility for biological fluid) for blood

• Involved using ethanol/acetic acid solutions which turned blue when the reagent and blood were added.

Hemastix Test

• Commercial test strip that can be used as a presumptive test for blood

• Designed to detect blood in urine

Phenolphthalein Test

Presumptive test that turns pink when blood is added to the reagent

Luminol/Flourescein Test

Presumptive blood test that causes light to be emitted from blood stain

Crystal Test

Presumptive test in which a positive result is the formation of a solid crystalline substance

Seminal Acid Phosphate

• Enzyme found in abundance in seminal fluid

• Commonly tests for semen

Alpha-Amylase

• Enzyme found in saliva

• Basis for presumptive tests for that saliva

  • Starch-iodide tests are common

Azostix

• Test used to detect urine

• Commercially used to detect blood in urine

  • Urine tests are inaccurate and not common in forensic science

Periodic Acid-Schiff Reagent

Presumptive test for the presence of vaginal material

Glycogenated cells are stained bright magenta

Hard, Smooth Surfaces (Glass, Smooth Tile) Create ______________ ______________

Little spatter

Rough Surfaces (Wood, Concrete) Create _______ ____ ______________

Lots of spatter