Crime scene investigators rely on a variety of techniques to help them determine how a crime was committed and who committed it. The analysis of physical evidence includes looking for fingerprints and DNA, and examining blood-spatter patterns to determine what type of weapon was used and the spatial relationship of the weapon to the victim. Bullet trajectory techniques complement the blood-spatter analysis, and digital photography helps investigators preserve the appearance of the crime scene for future analysis.
One of the most crucial techniques used by forensic investigators is to analyze physical evidence left at a crime scene. In order for physical evidence to be properly collected, the crime scene must be secured, protected and preserved by the first officer responding to the call. DNA, bloodstains, fingerprints and shoe prints are among the physical evidence investigators collect from the crime scene.
Evidence of violent crimes often includes blood spatters or blood stains. Crime scene investigators will pay close attention to the pattern of blood spatter to try to reconstruct events that took place during the crime. Certain weapons will create distinctive spatter patterns that may be crucial to the investigation. Interpreting a blood stain or spatter is a technique that is often performed by a forensic scientist who specializes in blood analysis.
Digital photography is an important tool in a crime scene investigation. Photographs and videos taken at the crime scene are used to help investigators piece together clues based on the exact appearance of the area where the crime took place. Often, photos are presented in court to authenticate other evidence and to present an accurate representation of the scene of the crime. In most cases, witnesses must testify to the accuracy of the digital photos or videos.
Crime scene investigators utilize bullet trajectory techniques to trace the path of the bullets and to determine the position of the victim's body at the time of the shooting. Depending on the type of crime scene they are dealing with, investigators may use fiberglass or metal rods and in some cases, wooden dowels, to insert into the bullet holes left in walls or objects. They then attach string to the rods to continue tracing the bullet's path based on the angle of impact. The string can be tied to PVC poles to help investigators determine the shooter's position and distance from the target. Other factors related to this type of investigation include the location of shell casings and the placement of the body.