But on to this month's topic: Blood.
Or more importantly: Blood Spatter. A lot of this is in point for so hopefully you can make sense of all this information. Next month I'm still looking for suggestions. Here are part one and two of the Forensic Friday Series.
What would you like to see in the coming months?
Again, thank you to El, without you nothing would be possible. Now, on with the show. You Comin'?
Blood Stain Pattern Analysis (BSPA) is the analysis of blood in various surfaces. From this you can learn
· what type of weapon was used
· how fast it was moving
· number of blows
· whether the assailant(s) was right or left handed
· where they were positioned in relation to the victim
· the order of wound infliction
· the type of injuries
· how long ago the crime was committed (tying back to the first Forensic Friday)
· whether or not death was immediate or delayed
Different methods are used to detect blood at a crime scene such as
· UV lights (something as simple a flashlight with a filter attached)
· Presumptive tests measure the properties of hemoglobin in the blood (though it can’t be determined if it’s human) (determine blood group)
· Luminol (a chemical sprayed – though substances such as cleaning products and paint can react poorly and destroy other evidence; false positives can occur in contact with certain substances such as starch)
· Fluorescein (chemical spray for fine stains or smears- glows greenish white)
There are different types of bloodstain patterns
· Passive Bloodstains
o Drops created by gravity
o Pool if the source is in one location
o Show movement in a series of drops (point of drop indicates direction, length of drop indicates speed.
· Projected Bloodstains
o Force is applied to the source of the wound (like a knife or bullet etc.)
o Low, medium or high velocity
o Expiratory blood from the nose, mouth or wound
· Transfer or Contact Bloodstains
o Smudged or wiped stains
o Caused by movement over or through a bloodstain
Spattered Blood is the random distribution of bloodstains that vary in shape and size. Forensic scientists use a method called “Stringing” by connecting and analyzing the distance and position or each stain.
The Origin or Source is the object or place where the blood spatter came from (like a bat for example)
The Angle of Impact is the angle at which a blood droplet strikes a surface. This is done by analyzing passive bloodstains.
Satellite Spatter is a drop from above (how a pool would start). The parent drop is the initial drop and the residual drops are called satellites. Spines are the pointed edges stain that radiate out from the parent drop. The further from the ground, bigger the spines will be. A rule of thumb: the larger diameter of the drop, the faster the drop was moving – but this also depends on the volume of the drop.
Surface also factors into stain and spine analysis. Smoother surfaces will create a smooth sphere even it comes from further than seven feet which is the maxed out height/velocity. Rough surfaces will cause spines. Carpet is tricky because the carpet will absorb the blood patterns.
In trails (or just one drop of blood), determining the direction the blood came from is essential. The narrow end of the blood drop (lengthwise) will point toward direction of travel. If the blood drops from a 90 degree angel (just standing or walking EXTREMELY slow) that’s when you’ll get your satellite spatter and the more acute the angle (60, 30, 10) the longer the tail will be.. The angle can be determined using trigonometry (just when you thought you were done with high school math).
Just for kicks: sine= Width/Length therefore arcsine = angle of impact
So after analyzing all the blood drops of width and length versus angle of impact you can determine the initial impact. By using string (or a laser) to measure lengthwise across several droplets of the blood, the point where they intersect is the point of origin.
Any diameter that measures one millimeter or smaller can be attributed to gunshot spatter. This is considered high velocity spatter as it often results in misting which are those tiny, less than 1mm droplets. Gunshots will result in both back spatter (where the bullet enters) and forwards spatter (where the bullet exits).
Medium velocity spatter measures at about 1-4mm. These are associated with beatings or stabbings. The first blow usually doesn’t result in spatter since there is no exposed blood. Castoff is also at medium velocity. This is blood flung off of a swinging object and can be useful in determining where the assailant and victim were positioned.
Low velocity measures at 4mm or greater. This is from walking and bleeding or from a still object. This will, eventually, create a pool of blood. Once a pool has been created, impression patterns can be created if, for example someone steps into the pool or a hair moves across the surface. Any transfer or disturbance of blood is recorded.
· Transfer is the transfer from a bloody surface to a secondary surface like placing a bloody hand on the wall
· Contact is an object making direct contact with blood such a shoe stepping through the pool
· Swipe is when an object moves across the surface like a hair and
· Wipe is when an object moves through the blood like a hand through the drop
Expiratory Bloodstains are the blood that appears (with saliva or nasal secretions) in events such as beatings or gunshot wounds and create a misting effect.
Arterial gushes are when an artery is hit (like a knife slicing across someone’s throat). The resulting spray pattern is called arterial gushing. Voids in spray can indicate where the attacker was standing or where something was removed from the scene after the event.
You can determine (well guesstimate) how long ago the blood left the body by examining how dry or how clotted it is. Smears in the clot can also indicate the time movement happened.