Halloween Murder in the Napa Valley
Interpreting blood spatter patterns is a both a science and an art, based on experience and interpretive ability. As a liquid, blood obeys the laws of physics and when force is applied to a body resulting in a spray of blood, the amount that sprays, the shape of the drops, the angle of impact, and the final location of a spatter will indicate a number of things: the blood's velocity, the type of weapon used, and even how many people were involved. The greater the force striking a person, the smaller the size of the spatter. Blood with more weight travels farther, but eventually it all curves downward if it doesn't impact somewhere, impelled by gravity.
Reading bloodstain patterns helps investigators figure out the positions of victim and attacker, and the stages by which they moved around, interacted, and struggled. Once the events are reconstructed, investigators can more effectively look for fingerprints, trace evidence, footprints, hair, and fibers. The assessment of bloodstain patterns will also limit the need to collect an overabundance of blood samples for DNA, and an accurate reconstruction helps determine if a witness or suspect is telling the truth.
The shape of the blood drop can also yield important information. The proportions reveal the energy required to disperse it in those dimensions, while the shape of a bloodstain can illustrate the direction in which it was traveling and the angle at which it struck a surface. Choosing several stains and using basic trigonometry enables the crime scene processor to devise a three-dimensional recreation of the area of origin from which a blood-letting event occurred.
In the Napa attack, there had been an attacker and two victims, who had been sleeping in adjoining rooms. The attacker had been wounded and lost blood, as did the victims, and identifying the three different blood types showed exactly where each person had been when wounded, and where they had gone from there. It appeared that Leslie had taken the first blow, attacked while asleep, but she had ended up face-down on a pile of clothing near the bed. Adriane appeared to have struggled with the attacker, possibly trying to save her friend before she finally drove him out and succumbed to her wounds. Along with the blood pattern evidence, Adriane showed a lot of bruising and defensive cuts on her hands.