Forensics Chapter 4: Crime Scene Reconstruction/Blood Patterns

reconstruction

the method used to support a likely sequence of evens by the observation and evaluation of physical evidence and statements made by those involved with the incident

bloodstain patterns can uncover:

1. the direction the blood came from
2. the angle the blood drop struck a surface
3. the location or position of a victim at the time of the attack
4. the movement of a bleeding individual
5. the number of blows to the victim
6. the location of an individual delivering blows

the harder and less porous a surface is...

the less spatter results

Angle of impact (blood spatter)

width of blood stain/length of blood stain

impact spatter

when an object impacts a source of blood

forward spatter

projected outward and away from the source

back spatter (blow-back spatter)

projected backward from the source

low velocity spatter

drops with diameters of 4 mm or more normally produced by an applied force of up to 5 ft/sec.

medium velocity spatter

drops with diameters from 1-4 mm with an applied force of 5 to 25 ft/sec.

high velocity spatter

drops with diameters of less than 1 mm from an applied force of 100 ft/sec or faster.

cast-off spatter

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

arterial spurt spatter

caused by an injury to the heart or a main artery and the pressure of the continuing pumping

area of convergence

the point on a 2d plane from which the drops in an impact pattern originated

area of origin

the area in a 3d space from which the blood was projected

gunshot spatter

fine forward spatter from an exit wound and back spatter from an entrance wound

drawback effect

depending upon the distance from the victim that the gun was discharged, some back spatter may strike the gunman and enter the gun muzzle.

expirated blood pattern

created by blood that is expelled from the mouth or nose from an internal injury

void pattern

created when an item is removed from the area after bloodstain spatter has been created

contact/transfer pattern

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

swipe pattern

caused by movement of the bloody object across a surface

flow pattern

made by drops or large amounts of blood flowing by the pull of gravity

pools

when blood collects in a level (not sloped) and undisturbed place

skeletonization

when the edges of a stain dry to the surface

drop trail pattern

formed by blood dripping off an object or injury. form a kind of line or path usually made by the suspect after injuring themselves or the victim or killing them

grid method

type of bloodstain documentation where a grid of squares of known dimensions are set up over the entire pattern

perimeter ruler method

type of bloodstain documentation where a rectangular border of rulers is set up around each pattern and a smaller ruler next to each stain