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Crime Scene Training

The New Detective DNA, Physical Evidence, Documentation, Photography

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Forensic Crime Scene Investigation Techniques

 

DNA Evidence

DNA evidence can be collected from virtually anywhere. DNA has helped solve many cases when imaginative investigators collected evidence from nontraditional sources.

Just as today's law enforcement officer has learned to look routinely for
fingerprints to identify the perpetrator of a crime, that same officer needs
to think routinely about evidence that may contain DNA. Recent
advancements in DNA technology are enabling law enforcement officers
to solve cases previously thought to be unsolvable. Today, investigators
with a fundamental knowledge of how to identify, preserve, and collect
DNA evidence properly can solve cases in ways previously seen only on
television. Evidence invisible to the naked eye can be the key to solving a
residential burglary, sexual assault, or child's murder. It also can be the
evidence that links different crime scenes to each other in a small town,
within a single State, or even across the Nation. The saliva on the stamp of
a stalker's threatening letter or the skin cells shed on a ligature of a
strangled victim can be compared with a suspect's blood or saliva sample.
Similarly, DNA collected from the perspiration on a baseball cap
discarded by a rapist at one crime scene can be compared with DNA in the
saliva swabbed from the bite mark on a different rape victim.

Types of Evidence

  • Impressions include fingerprints, tool marks, footwear, fabric impressions, tire marks and bite marks.
  • Forensic Biology includes blood, semen, body fluids, hair, nail scrapings, blood stain patterns,
  • Trace Evidence includes gun shot residues, arson accelerant, paint, glass and fibers.
  • Firearms includes weapons, gun powder patterns, casings, projectiles, fragments, pellets, wadding and cartridges.
  • Question Documents

Crime Scene Investigation

Most police investigations begin at the scene of a crime. The scene is simply defined as the actual site or location in which the incident took place. It is important that the first officer on the crime scene properly protect the evidence. The entire investigation hinges on that first person being able to properly identify, isolate, and secure the scene. The scene should be secured by establishing a restricted perimeter. This is done by using some type of rope or barrier. The purpose of securing the scene is to restrict access and prevent evidence destruction.

Once the scene is secured, the restrictions should include all nonessential personnel. An investigation may involve a primary scene as well as several secondary scenes at other locations. On major scenes a safe space or comfort area should be designated at the crime scene to brief investigators, store needed equipment, or as a break area.

In critical incident management the protocol that is being taught today identifies a three layer or tier perimeter. The outer perimeter is established as a border larger than the actual scene, to keep unlookers and nonessential personal safe and away from the scene, an inner perimeter allowing for a command post and comfort area just outside of the scene, and the core or scene itself. An extreme advantage will be seen by taking the time to properly teach the uniform officers and first responders to evaluate and secure the scene.

Forensic Photography
Blood Spatter
Sharp Trauma
Blunt Truma
 

Physical Evidence at a Crime Scene

Evidence used to resolve an issue can be split into 2 areas. Testimonial evidence and physical evidence. The testimonial evidence would be any witnessed accounts of an incident. The physical evidence would refer to any material items that would be present on the crime scene. These items would be presented in an issue or incident to prove or disprove the facts of the issue. What will evidence collected at a scene do for the investigation :

  • May prove that a crime has been committed.
  • Establish any key elements of a crime.
  • Link a suspect with a scene or a victim.
  • Establish the identity of a victim or suspect.
  • Corroborate verbal witness testimony.
  • Exonerate the innocent.

 
 
 
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