" Forensics" Reconstructive Patterns

reconstruction evidence provides information about the events preceding, occurring, during and after commission of a crime (Nordby). On the other hand, associative evidence is the tools used for reconstructing a crime scene. They generally locate evidence that can be used to associate or disassociate a suspect to a crime. Bullets, bodily fluids, firearms, and fingerprints are examples of associative evidence. In addition, Biological evidence is very useful especially if the criminal is a repeat offender. This is because; when an offender is charged with a crime DNA specimens are taken and entered into the system. If a repeat offenders bodily fluids (such as; blood or semen) are found at the scene and sent to Forensic laboratories when they DNA is processed and results become available the offender is caught. After that it is just a matter of locating the criminal to charge them with the crime.  

Furthermore, there are many other ways of processing evidence.  Evidence that can be collected from a crime scene Include physical evidence, and trace evidence. Some examples of physical evidence are tracks and fingerprints. Fingerprints can also be very useful if the suspect is a repeat offender because; along with DNA samples fingerprints are also recorded in the system. Tire tracks can be useful because it leaves behind a pattern showing some or all of its surface characteristics, known as an impression. The collection and analysis of impression evidence found at the scene of a crime can often be very important to an investigation. The collection of objects, marks and impressions that make up the physical evidence of a crime is a specialized task. The general principles of preserving physical evidence and assuring a secure chain of custody apply whatever the crime  (http://www.enotes.com/forensic-science/physical-evidence).

 Locard's Exchange Principle dictates that evidence, both physical and biological, is to be found at the scene of a crime because the perpetrator always leaves something behind by having contact with victims and objects there. (http://www.enotes.com/forensic-science/physical-evidence)

''Forensics'' Blood Stain Patterns

 In 1955, the first meaningful achievement of bloodstain evidence was credited to Dr. Paul Kirk of the University of California at Berkeley (Nordby).

First of all, blood contains a fluid portion we call plasma. Plasma contains natural segments of erythrocytes, leukocytes, and platelets. The nuclei of the leukocyte (white blood cells) are our source to DNA evidence. Furthermore, blood is similar to common fluids however, blood is held together by powerful cohesive molecular forces that generate a surface tension within each drop and on an external surface (Nordby).

Moreover, surface tension is a great way to determine the characteristics of bloodstain patterns. For instance, if a single drop of blood fell vertically on a nonporous surface there would be little to no spatter. In contrast, if the blood fell vertically on a porous or rough surface nine times out of ten there will be a significant amount of spatter. The geometry of determining an individual bloodstain pattern can be very complex. The direction of travel, area of origin and angle of impact are important factors in reference to determining the area of convergence to blood stain patterns (Nordby).

Not to mention, bloodstain spatters vary in size.  After identifying bloodstain spatters; gathering medical, scene, and case related evidence; determining the mechanism category becomes easier for the analyst to establish specifics.  Categories of blood spatters are based on the mechanisms. Such as:

Secondary mechanisms                 Impact mechanisms            Projection mechanisms

Satellite Spatter                                   *Gunshot                                *Cast off

*Beating/Stabbing                  *Arterial

*Power tools/etc.                    *Expirated

Furthermore, arterial punctures can produce very large quantities of blood. When an artery is punctured it is usually obvious. This is because; arterial punctures varying from large gushing or spraying patterns to small spray patterns are obvious. Like, if an individual was stabbed in the neck and an artery was punctured this type of injury would result in a large amount of spraying or gushing from the body; developing obvious patterns of an arterial spurt (Nordby).

Lastly, transfer bloodstain patterns are when an object wet comes in contact or whipping with an unstained object or secondary surface. Transfer patterns can be a very useful part of solving an investigation. If a suspect dropped a knife used in a murder in the woods and it was recovered and if trace evidence were found, the evidence can be examined to rule out the suspect involved (Nordby).