The government serves as the plaintiff in a criminal case since a crime is an offense committed against society, and it is the state that starts a criminal prosecution. The government acts on behalf of the society. In the United States, the government prosecutes the case through the United States Attorney’s Office, if a person has committed a federal crime.
The government acts as the plaintiff in a criminal case because the crime that was committed is assumed to be against the citizens of a state, or country, as a whole. The offence of the criminal is against the laws of that jurisdiction.
This action removes the responsibility of capturing and punishing the criminal from that individual victim. It also stops "vigilante justice," or a civilian acting in a law enforcement capacity without legal authority.
