When you’re called to a crime scene, you never know what you’re going to find. But no matter the scene, it’s important to recover as much evidence as possible. Sometimes we get so caught up in looking for DNA and other obvious evidence that we overlook other evidence that can be just as important. Impression evidence is a good example. Collecting impression evidence is definitely worth the effort—once you do so, you have duplicate evidence that can help make your case.
When you arrive at the scene, carefully secure the perimeter and limit access. If impression evidence is present, you must do everything possible to preserve it. Next, work on locating the evidence. Impression evidence includes footprints, tire tracks, and tool marks. Often this evidence will be clearly visible. Tire tracks left in mud are a good example. But in some cases, this evidence may be hard to spot. Begin by thinking about the likely movements of a suspect at the scene: How did he enter? Where did he go? How did he exit? Examine all of these points for impression evidence. When you’re outside, look for tire tracks and footprints in the surrounding area. Pay special attention to entryways and windows. Are there signs of forced entry? These are the places where you might find tool marks. Don’t forget to examine hard surfaces such as window ledges, car doors, counter tops, chairs, carpets, tile, and wooden floors for footprints. These types of prints can be difficult to spot; you need to get down low to the surface with your flashlight. Hold the beam at an angle so that the light will cast shadows, allowing you to see the prints.
In many cases, CSOs simply photograph impression evidence once they find it. While it’s true that you absolutely must document all evidence you find with photographs, you shouldn’t stop there. You can collect, and thus duplicate evidence, by creating casts of three dimensional impressions (tool marks and footprints and tire tracks left in mud, sand, or snow) and electrostatic lifts of two dimensional impressions (dust footprints).
Figure 1: Tool mark lifted with AccuTrans
Always document your evidence with photographs before you try to collect it. Collecting impression evidence can be crucial to your case, but if you mess up during the process and you haven’t photographed the evidence, then you’re left with nothing. Take the time to do the job correctly. Take overall and medium range shots that show the location of the evidence in the scene, then move to close ups of the evidence itself. Remember that the quality of the close ups is crucial to the examiner. You need to capture as much detail as possible in your shots so that the examiner can make a comparison with the actual object.