Final answer:
Police gather and analyze evidence left behind at a crime scene to understand what happened and identify the perpetrator.
Step-by-step explanation:
When studying a crime scene, police gather evidence to piece together what happened at the scene. They analyze the physical evidence left behind, such as fingerprints, DNA, and footprints, to identify the perpetrator and understand how the crime took place. For example, DNA evidence found at a crime scene can help link a suspect to the crime. Additionally, examining the location, objects, and patterns at the scene can provide further insights into the motive and method of the crime.