How do the Police Investigate Crimes?
When a crime is committed, the police must determine who committed it so that the criminal can be prosecuted and brought to justice. But how do the police go about investigating these crimes?
Crimes in Progress
As soon as the police receive a call that a crime is in progress, they send officers to the scene of the crime as soon as possible. The officers may be able to catch the criminal right on the scene. The officers will then arrest this person and take her to the police station or the county jail for booking. Before leaving the scene of the crime, the police or their employees will often do a site investigation by taking pictures and taking any objects they think are connected to the crime for evidence. Almost everyone who was at the scene will write a report, including their personal observations, the names and contact information of any potential witnesses, and any items that they took from the scene.
If a crime was not observed in progress and was particularly serious or complicated, the police may assign the case to a detective. She will then manage a team of investigators to develop a list of suspects and find the actual criminal defendant. The detective may collect forensic evidence, like fingerprints, blood, or saliva found at the scene and send them to labs for analysis. She can also speak to witnesses to try to piece together what happened.
At all times, the police and their employees must obey the Fourth Amendment's rules for permissible search and seizure. This means that generally, if the police want to search any private property, they must first obtain a warrant which shows that they have probable cause to believe that they will find evidence that will help solve the crime.