Crime Scene Reconstruction and Blood Spatter analysis
Basic Steps:
1) Observe everything
2) Recognize evidence--note anything out of place, suspicious or obvious
3) Document it with notes, diagrams and photos
4) Collect evidence and place markers where it was found
5) Evaluate it for as much information as possible
6) Come up with a working hypothesis of how the incident occurred.
7) Test the hypothesis against the evidence often by simulating what is assumed to have a happened and see how it plays out
8) Use everything available to reconstruct the action at the scene and write up a report
The type of reconstruction undertaken is base on the nature of the crime, the incriminating factors and the questions that need to be answered.
Some analysts say that there are five common ways to approach reconstruction:
* Specific incident--traffic accidents homicide, arson, rape
*Specific event--How some part of the incident happened in a sequence or determining position of participants
* Analysis of a specific type of physical evidence--fire arms, glass, handwriting, blood spatter
* Partial case reconstruction--perhaps concentrating on only one room and approaching it with more than one method.
* Specialized determinations within a crime scene--criminal profiling, modus operandi, signature analysis.
Pattern evidence is also key in reconstruction.
It's the kind of evidence that's produced and from forcible contact with an object or person
That means some type of violence and among the kinds of pattern evidence we have:
* Blood spatter patterns
* Glass Fractures
* Print Impressions
* Psychological patterns(signature)
* Modus Operandi (MO)
* Fire burn or powder residue patterns
* Projectile Trajectories
* Skid Marks
Blood Spatter Patterns(BSP)
Blood Spatter is an important indicator at a crime scene because it usually tells an investigator what type of weapon caused the injury.
High-Velocity blood spatter typically results from a gun shot wound.
Medium-Velocity spatter comes from a stab wound or blow from a blunt instrument.
Low-Velocity spatter is the result of dripping blood.
Liquid blood dries fairly quickly, clotting first on the surface exposed to air and then continuing to dry from the outside in. It is this propensity of blood to clot, a fairly complex chemical and biological process, that prevents uf from bleeding to death following minor cuts or bruises.
Liquid blood is thin and light red in color. Newlyclotted blood turns a darker red, shading to red-brown. A dried blood stain can be any number of color's from black to transparent, including brown, blue, green, grey and white. The color is determined by the physical and chemical composition of the surface upon which the blood falls, the thickness of the stain itself, and outside factors such as temperature, humidity and sunlight.
The appearance of a drop of blood that has landed on a surface will vary according to the height from which it was dropped and the surface upon which it lands. On comparatively smooth, flat horizontal surfaces, the drops will be round if the fall is short, jaged edges will begin to appear as the height is increased, and the jaggedness will increase with height. If the height is higher than six feet of so, the drops will break up into smaller drops.
If the object emitting the blood is in motion, the blood drops will be oval and have little tails, which will project in the horizontal direction that the drop was moving. Falling liquids have a characteristic tear-drop shape, tapering toward the top.
Since the top lands last, the taper is forward of the main part of the drop. Blood splatter on a wall can indicate whether the murder weapon was held in the killer's right or left hand.
A path of drops several feet appart that sown an elongated shape indicates that someone who was bleeding was also running. If they are closer together and more rounded, but still in a path, the person was moving more slowly. Drawing a line through several successive stains will indicate the direction in which the person was moving. If elongated, the narrow end points in the direction of travel.
The greater the force striking someone the smaller the size of the spatter.
Punching someone in a way that draws blood will result in a larger surface than a bullet produces.
Blood with more weight travels farther but it only travels so far in a straight line before it curves downward.
In the 1930's Scottish Pathologist John Glaister classified blood splashes into six distinct types:
1) Drops on a horizontal surface
2) Splashes from blood flying through the air and hitting a surface at an angle
3) Pools of blood around the body
4) Spurts from a major artery or vein
5) Smears lift by movement of a bleeding person
6) Trails from a body dragged or carried or a bleeding person in motion.
The rule of thumb when dealing with a generally smooth and nonporous surface:
1) If blood falls a short distance around 12 inches at a 90 degree angle the marks tend to be circular
2) If blood drops fall several feet straight down the edges may become crenellated and the farther the distance from the source to the surface the more pronounced the crenellation
3) A height of 6 feet or more can produce small spurts that radiate out from the main drop
4) If there are many drops less than an eighth of an inch across with no larger drops than it may be concluded that an impact produced the blood spatter
5) If the source was in motion when the blood leaked or spurted or if the drops flew through the air and hit an angled surface the drops generally look stretched out exclamation marks. The end of the stain that has the smallest size blob indicates the direction in which the source was moving.
Source Information--How to Solve a Murder: The Forensic Handbook. Michaei Kurland. 1995. Simon & Schuster.
The Forensic Science of CSI. Katherine Ramsland. 2001 The Berkely Publishing Group.
Signature Killers. Robert D. Keppel, Ph.D with Willian J. Birnes. Pocket Books 1997
