 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)

 Hemastix – if red stain is blood - plastic strip treated w/ reagent, moistened w/ dH 2 O - if turns green – blood  Luminol – mixed w/ H 2 O 2 – is oxidized - to test large area for blood - emits light

 Leucomalachite green – similar rxn - in presence of iron, turns blue-green  Kastle-Meyer test – - phenolphthalen turns pink

 Photograph & document scene  Collect samples of blood separately from others  If on object, collect whole object  If on large object, collect only blood

 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

 = 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

 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

 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

 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

 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

 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

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

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

 Arterial spray - based on heartbeat pattern

 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

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