The first step in gathering evidence is finding it, and that means taking an orderly approach to searching the crime scene. Many items, such as corpses and weapons, may be readily visible, but others, particularly smaller materials or bits of trace evidence, require diligence on the part of investigators.
In homicides, investigators target points of entry and exit and the area near the body; in robberies, open safes, cabinets, or drawers are good starting points.
The way investigators search for evidence depends upon the size and physical layout of the area in question. Scanning the floor of a broom closet for fiber evidence is much different than searching a half-acre lot for a shell casing. Yet in both situations the search must be thorough and orderly.
When searching a crime scene for trace evidence, investigators typically follow a geometric pattern (see the following figure). They may use a crisscrossing grid, a shoulder-to-shoulder linear pattern, or expanding or contracting spiral patterns. The spiral may begin at the body or the cracked safe and move outward, or it may begin at the periphery of the crime scene and circle inward toward the spot where the actual criminal act took place.
Larger areas are first divided into quadrants or zones so that each smaller area can be scanned using one of these methods. The goal is to carefully search every square inch of the target area.
