Plasma (mainly water) Solid materials (blood cells) Erythrocytes – red; carry oxygen Leukocytes – white; fight infection Platelets - clotting Blood composition:
Type O is considered the “Universal Donor” • Type AB is considered the “Universal Recipient”
Rh factor (D antigen) • if a person has this antigen, they are considered Rh + • if not, they are Rh –
Secretors • blood type antigens found in body fluids • ~80% of the population
1. Is it blood? • Kastle-Meyer color test
1. Is it blood? • Luminol Test
2. What species did it come from? • Microscopic examination
Human or Animal? • This is frog blood. • Notice the nucleus is present in the cells.
Human or animal? • These are human red blood cells. • Notice they don’t have a nucleus.
2. What species did it come from? • Precipitin test
3. Significance of stain patterns in blood • Confirms or refutes theories of witnesses, suspect(s) and/or victim(s) • Helps to develop or eliminate leads • Helps to reconstruct the events which led to the creation of stain patterns present at the scene.
What blood evidence can tell us: • The points of origin of the blood stain patterns • Number of blows delivered in an attack • Sequence of events • Positions of person and objects
What blood evidence can tell us: • Whether something was moved • Whether someone or something was blocking the spatter • If there were struggles or if someone/something was dragged • The impact angle of the drops • Location of blood source
Surface Effects • Blood droplet that fell on glass
Surface Effects • Blood droplet that fell on linoleum
Surface Effects • Blood droplet that fell on concrete
Low Velocity spatter • Usually 4 mm in size and larger • Force up to 5 feet/second
Medium Velocity Spatter • 1 to 4 mm in size • Force of 5 – 25 feet/second
High Velocity Spatter • 1mm in size and smaller • Force of 100 feet/second &greater • Mistlike
Transfer Patterns Hand print Shoe Print
Transfer Patterns • Created when a wet, bloody surface comes in contact with a second surface and leaves a distinct pattern Hair swipe
Transfer patterns From a knife
Transfer Patterns Screwdriver