lecture 6 blood spatter analysis

crime scene reconstruction

the reconstruction of events that occured before, during, and after the commision of the crime. Based on physical evidence and statements. made by individuals involved with the incident, require team effort

reconstruction is based on

• physical evidence

• forensic lab results

• investigators common sense and experience

• witnesses statements

• statistical analyses

Crime scene reconstruction consists of

1. wound patterns

2. gunshot residue patterns

3. glass fracture patterns

4. fire burn patterns

5. blood spatter patterns

Blood stain patterns can reveal

• direction of origin of bloodstain

• angle of impact of bloodstain

• speed of bloodstain from its origin

• location and position of victim/suspect

• movement of victim/suspect from the crime scene

• minimum number of blows/shots

Direction of origin of bloodstain

the tail tells the tale, narrow end of blood drop points in the direction of blood.

90 degree fall bloodstain

when a blood droplet strikes a surface from 90 degrees it creates a circular stain, there will be no long or short exes and spines, scallops, and satellites will occur moderately. very little difference will be discernable between drops that impact anywhere between 90 and 75 degress.

Harder nonporous surface: 90 degree fall

glass or smooth tiles, causes less spatter around the stain

rough surface: 90 degree fall

wood/cloths causes ireegularly shaped stain with serrated edges sometimes satellite spatter .

90 degree fall effect of height

dimater of the bloodstain increases with height but no changes in diameter after 7 feet.

45 degree fall

as the angle of impact gets lower and lower, generally between 75 and 40, the elongation of the spatter stain becomes more and ore apparent, and the spines, scallops, and satellites are more focused and more to the side opposite the angle of impact.

25 degree fall

at highly acute angles, generally below 40 degrees, the nature of the outflow changes. A single satellite tends to form, acting essentially like a second spatter emenating from the first one, causing a distinctive exclamation point.

area of convergence

think of the dexter red strings, the area on a 2D plane, from which bloodstain pattern originated.

area of origin: string method

1. place pole at an area of convergence

2. attach one end of string next to each droplets

3. using protractor, align string in line with angle of impact

4. attach other end of string to the pole

5. area of origin is an area where all strings appears to meet.

impact bloodstain patterns; low velocity spatter

applied force of <5 ft/sec

bloodstain diameter > 3mm

normally, produced by gravity alone, object dropping into a blood pool

impact bloodstain patterns; medium velocity

• applied force of 5-25 ft/sec

• bloodstain diamete of 1-3 mm'

• blunt force trauma

impact blood stain patterns;high velocity

• applied force of >100 ft/sec

• blood stain diameter <1mm

• gunshot exit bloodstain pattern, bloodstain patterns by explosion

gunshot spatter

back spatter is created where the bullet enters, and forward spatter is created where the bullet exits.

• backspatter are generally fewer and smaller than forward spatter

drawback effect

when backspatter strikes gun man and enters the gun muzzle.

cast off spatter

created when blood-covered object flings blood in an arc onto a nearby surface.

bloodstain arc pattern

helps in determination of direction in which impact object was moving

number of arcs

can help in determination of minimum number of blows delivered

size of the droplets for cast-off spatter

helps in determination of object used for creation of patterns

• smaller drops from small pointed objects

• larger drops from large blunt objects

arterial spray spatter

A blood spatter pattern resulting from a bleeding artery, typically characterized by a misty or fine spray, often seen in cases of severe trauma.

expirated blood patterns

blood from mouth, nose, and lungs under high pressure.

void patterns

created when an object blocks the deposition of blood spatter onto a target surface.

contact/transfer patterns

when an object with blood on it touches one that does not have blood on it.

simple transfer patterns

no movement of the object

swipe patterns

results from the transfer of blood from a blood-bearing surface onto another surface

wipe patterns

results from an object moving thorugh a pre-existing bloodstain

flows patterns

movement of small or large amount of blood because of gravity. clotting time outside the body ranges from 3-15 minutes, the flow direction may show movements of objects or bodies while the flow was still in progress or after the blood dried.

blood pools

• a pool of blood occurs when blood collects in a level (not sloped) and undisturbed place

• skeletoniztion occurs when the edged of a stain dry

• usually within 50 seconds of deposition but may take longer time for larger volumes of blood

drip trail patterns

series of drops that are separate from other patterns, formed by blood dripping off an object or injury, the stains form a kind of line or path usually made by the suspect after injuring or killing the victim. or injuring themselves, show direction and speed of movement.

Documenting bloodstains: grid method

a grid of squares of know dimensions are set up over the entire patter using string and stakes. Overall, medium range, and close up photographs taken with and without the grid.

Documenting bloodstains: perimeter ruler method

a rectangular border of rulers is set up around each pattern. Large ruler show scale in overall and medium range and a smaller ruler show scale in close-up photograph.