blood at scene – used to id victim or perpetrator blood type can exclude nuclear dna –...

FORENSIC IMPLICATIONS OF CIRCULATORY SYSTEM

Blood at scene – used to ID victim or perpetrator

Blood type can exclude Nuclear DNA – individual evidence – can

ID (RBCs – no nucleus or DNA; WBCs – have it)

Presumptive Tests

Hemastix – if red stain is blood- plastic strip treated w/ reagent,

moistened w/ dH2O- if turns green – blood

Luminol – mixed w/ H2O2 – is oxidized- to test large area for blood- emits light

Presumptive Tests

Leucomalachite green – similar rxn- in presence of iron, turns blue-green

Kastle-Meyer test – - phenolphthalen turns pink

Scene

Photograph & document scene Collect samples of blood separately from

others If on object, collect whole object If on large object, collect only blood

Scene

To collect dried blood – - use wet swab- use fingertip tape to lift stain- scrape blood into paper bag

If wet blood, need to dry first

Collect evidence from suspect Samples = control or known sample for

comparison Used to make a DNA profile to ID

Lividity

= pooling of blood in the direction of gravity

Livor mortis = postmortem change in color caused by lividity

Appears 30 min – 2 hours after death Not fixed yet – pooled blood can shift if

pressed Fixed after 12 hours – irreversible and

permanent

Lividity

B/c fixed – can be used to determine if body was moved after death

Patches of lividity in different areas of body indicate body was moved

After fixed, check position of body with lividity pattern

Lividity

Bluish-purple to reddish-purple near ground

Becomes darker over time b/c oxygen separates from hemoglobin -

> purple pigment (deoxyhemoglobin) Areas away from ground - pink

Clues from Lividity

Bright red - CO poisoning Bright pink – hypothermia, body

refrigerated shortly after death, cyanide poisoning

Dark brown – lethal doses of nitrates, aniline, & potassium chlorate (forms meth-hemoglobin)

If arm or leg hanging when person dies, petechiae (= small red dots underneath surface of skin) may show

Blood Spatter

Position of victim & perpetrator Use laws of physics Blood – high viscosity (= liquid’s

resistance to flow) Blood – high surface tension – allows

blood to retain its shape when contacts other object

Blood Spatter

Velocity blood travels as it leaves body combines with gravity producing a certain path

Low-velocity spatter- if person moves after losing blood

from stab wound, blood falls down large droplets

Blood Spatter

Medium-velocity spatter- from blunt force trauma - blood spurts out from body

Blood Spatter

High - velocity spatter- from gunshot wounds- tiny droplets, like a fine spray

Blood Spatter

Arterial spray - based on heartbeat pattern

Blood Spatter

Useful in determining: - position of victim - type of weapon or tool used - # of times victim was hit, shot, or stabbed - if victim moved after assault

Blood Spatter

After evaluation, may determine: Events of crime Sequence of events Who was or was not present