A perpetrator is someone who commits a crime or does something harmful and wrong. When police investigate a robbery, they're trying to find the perpetrator: the person who actually broke in and stole things. When a principal investigates vandalism at school, she's looking for the perpetrator who spray-painted the walls.

A perpetrator is the person who actually committed the wrongdoing and bears responsibility for it. If someone breaks your bike lock and steals your bicycle, that person is the perpetrator of the theft.

You might hear perpetrator in news reports about crimes, or in detective stories when investigators say they're “searching for the perpetrator.” It's a formal word that emphasizes the seriousness of harmful actions and the importance of holding the right person accountable.

The word focuses on who did it rather than why they did it or what should happen to them. A perpetrator might face consequences ranging from having to apologize and make things right to serious legal punishment, depending on what they did.