Police and reporters in the United States often use the word suspect as a jargon when referring to the perpetrator of the offense (perp in dated U.S. slang).
However, in official definition, the perpetrator is the robber, assailant, counterfeiter, etc.—the person who committed the crime.
[1] A common error in police reports is a witness description of the suspect (as a witness generally describes a perpetrator, while a mug shot is of a suspect).
[citation needed] Under the judicial systems of the U.S., once a decision is approved to arrest a suspect, or bind him over for trial, either by a prosecutor issuing an information, a grand jury issuing a true bill or indictment, or a judge issuing an arrest warrant, the suspect can then be properly called a defendant, or the accused.
Only after being convicted is the suspect properly called the perpetrator.