How do the Police Investigate Crimes?

Created by FindLaw's team of legal writers and editors.

When police officers are called to a crime scene, they may be lucky in that the perpetrator is still on the premises. In that case, the police take the criminal away and focus on building a case against them that stands up in court. But what about crimes where the criminal is long gone. How do the police investigate and solve that crime?

The primary tools that police have when investigating crimes are interviews or interrogations and collecting physical evidence. They then use the information that they have collected to piece together a possible scenario as to what happened that the collected evidence will support.

So how do the police investigate crimes? Read on to learn more about the basic police investigation steps that are used to build a criminal case.

Police Investigations: The Crime Scene

As soon as the police receive a call that a crime has been committed or is in progress, they send officers to the scene. The officers may be able to catch the criminal right on the scene. The officers will then arrest this person and take them to the police station or the county jail for booking.

However, even if the police caught the perpetrator red-handed, they will still collect evidence at the scene of the crime to support a criminal sentence. This evidence collection will include interviewing all of the potential witnesses at the scene. A site investigation will also be conducted, which may include taking pictures, measurements, taking forensic evidence, making general observations, and taking objects that may be connected to the crime.

At all times, the police and their employees must obey the Fourth Amendment's rules for permissible search and seizure. This means, generally, that if the police want to search any private property, they must first obtain a warrant or have probable cause that would allow a search without a warrant.

Police Investigations: Interviewing Witnesses

When the police officers conduct interviews, they're looking to establish the facts of the case, trying to figure out what happened and who might be responsible. Often, they'll interview witnesses separately so that they can have each person's individual recollection of the events.

The police will want to talk to people who have personal knowledge of the crime. In order to have personal knowledge, the witness needed to have seen, heard, smelled, tasted, or touched something first hand. The police will carefully document these witness statements along with the police officer's observations about the witness, so that the information will be available to future police officers, detectives, and prosecutors.

Police Investigations: Law Enforcement Observations

A key component of any criminal investigation is the observations of the police officers. Police officers are trained to observe and notice details. They will note the position of weapons, blood stains, clothing, weather and any other detail that might explain the crime or the criminal behavior.

Police Investigations: Physical and Forensic Evidence

The police will also collect physical evidence at the crime scene. This may include taking photographs, measurements, fingerprints, blood samples, and taking any objects that may be related to the crime. Each bit of evidence must then be properly recorded and documented. Physical items will be collected using gloves to preserve fingerprints and to limit contamination. If the crime warrants it, forensic evidence, like fingerprints, blood, or saliva found at the scene will be gathered and sent to labs for analysis.

The evidence items will be placed in a special bag that will be properly marked so it can be identified later. The chain of custody for each piece of evidence will be established starting with the person who collected it and then each transfer of that evidence will be documented to establish an unbroken chain from the time of collection to presentation at trial.

Police Investigations: Custodial Interrogations

The go to tool for most criminal investigations is the interrogation of suspects with the intention to trying to get a confession. While, forensic evidence receives lots of attention and is a valuable weapon in the war on crime, it is expensive and time consuming. An interrogation will often result in results much faster and certainly much cheaper.

Police officers and detectives are skilled interrogators. They have studied human behavior and body language. Interrogation is a science. Detectives know how to gain a suspect's trust and how to manipulate them into a confession. While the police must not violate a person's Miranda and constitutional rights in order to obtain a confession, they are still allowed a lot of latitude. For instance, the police can lie to a suspect. They also can engage in subterfuge or trick a suspect.

Want to Learn More About How the Police Investigate Crimes? Talk to an Attorney

Police investigations are an important part of the criminal justice system, but law enforcement can make mistakes, sometimes resulting in an innocent person going to prison. There are also important legal guidelines that police officers must follow when investigating crimes. If you're the subject of a police investigation, you should speak to a skilled criminal defense attorney who can ensure that your rights are protected and who can be your watchdog during any investigation.

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