5 types of pattern evidence all investigators should know
While all evidence at a crime scene is important and must be considered, pattern evidence requires careful analysis — and sometimes specialized training — in order to properly interpret it
Whenever a crime is committed, it is incumbent upon police officers and investigators to determine what happened. As a matter of standard practice, witnesses are interviewed in order to elicit their story. Well, there is one witness that can never be spoken to, yet still has a story to tell: the silent witness to the truth. Every crime scene has a story and through careful assessment, analysis, and evidence collection/testing, the story will often unfold.
Each crime scene is different and will be comprised of a variety of evidence to consider. Here, we focus on five types of pattern/impression evidence and some of the information that may help tell the story.
Pattern evidence, while common, is sometimes taken merely at face value because properly interpreting it may require some additional training. And those who take the time to educate themselves will glean a great deal of information and reap the rewards of understanding pattern and impression evidence as they relate to the events of a crime. The following are some examples of pattern/impression type evidence and just some of the information that we can obtain from our “silent witnesses.”
1. Tire Tracks and Marks
Tire tracks are often found at the scene of a crime and typically leave a tread impression or marking that may allow officers or investigators to learn:
• The type and class of tire
• Who manufactures/sells such tires
• What vehicle makes/models typically use such tires
• Location of the vehicle and/or direction of travel to or from the crime scene
• Number of vehicles involved
• Characteristics unique to the manufacturing process or wear patterns/defects in a particular tire
• Even more information at vehicle crash scenes including possible speed and if brakes were applied
2. Shoe Prints and Impressions
Like tire tracks, shoe prints are often left at a crime scene. Some suspects may attempt to “cover their tracks” by wiping down their fingerprints, but they often forget about shoe related evidence. Shoes are a great source of information. For both tires and shoes there are extensive make/model/manufacturer databases that can be searched. From shoe prints and impressions officers can discover:
• Number of potential suspects
• Suspect’s point of entry or exit and/or direction of travel
• Prove or dispel a suspect’s alibi
• Where shoes are sold
• Unique characteristics such as style, manufacture markings, defects, or wear patterns (recall bloody shoe prints in the O. J. Simpson case and the unique Bruno Magli shoes said to have made them)
• Shoe size can be correlated to estimating a suspect’s height
• Determine if suspect was running or walking
3. Finger and Palm Prints
Fingerprints are another form of pattern evidence and one’s frequently encountered at crime scenes.
• Obviously a reliable means of suspect identification
• Also may indicate suspect’ travel throughout a crime scene
• Not only is presence of finger/palm prints at a scene important but so is placement; may help to determine what suspect was trying to do, such as open a window or hold open a door while entering or leaving a scene
• When properly handled, a potential source of suspect DNA
4. Blood Stains
Blood stains will vary but may consist of transfer type stains, spatter, drops and even voids. Proper interpretation of blood stain evidence requires considerable training but a lot can be learned from this form of pattern evidence.
• Potential object used: gun, impact weapon, etc.
• Level of force used
• Estimated number of blows
• Angle of impact
• Source (arterial, lung, etc.)
• Relative location of victim and/or suspects throughout the scene
• Direction of travel
Yet another source of pattern evidence is glass. Unfortunately, glass often shatters leaving only small shards. This is still a helpful form of evidence depending on where the glass is located at the scene and whether or not the suspect, once identified, has any glass in or on his or her clothing. However, there are times when glass fractures rather than shatters and the radial or concentric patterns produced can tell a story.
• Direction of impact (inside or outside)
• Approximate angle of impact
• Approximate force used
• Sequence of firing – from firearm, BB/Pellet gun, etc…
• Intensity of heat in fire/arson cases
While all evidence at a crime scene is important and must be considered, pattern evidence requires careful analysis — and sometimes specialized training — in order to properly interpret it. When such evidence is properly interpreted it can provide a great deal of helpful and admissible investigative information.
Every officer and investigator should seek opportunities to further their education and understanding of specialized investigative techniques and evidence analysis. I cannot emphasize enough the importance of properly responding to, assessing, preserving, and interpreting a crime scene. The actions of the first responding officer cannot be overstated as there is nothing an investigator can do after the fact to restore the preliminary condition of a crime scene. The less things are disturbed pre-analysis, the greater your opportunity to obtain an accurate story.
Just as witnesses may sometimes be deceptive, a crime scene can also be misread if one is not careful. Do not limit yourself to only one possibility, train of thought, or hypothesis. Consider all possibilities in the case as you formulate a hypothesis and then test that hypothesis before arriving at a confident theory.
Remember, a crime scene many contain glass shards, fingerprints, tire tracks, or other evidence, but these are just a part of the big picture. Naturally, your final theory should consist of a totality of the information gathered during the entirety of the investigation and not solely what was discovered at the crime scene.