A criminal investigation is an official effort to uncover information about a crime. There are generally three ways that a person can be brought to justice for a criminal act. First, and probably the least likely, the individual will be driven by his conscience to immediately confess. Second, an officer of the law can catch him in the act. Third, and most common, a criminal investigation can identify him as suspect, after which he may confess or be convicted by trial.

In most cases, when a crime is committed, officials have two primary concerns. They want to know who committed the crime, and what the motive was. The reason why a person breaks a law is called the motive.