> Arrests need warrants. Arrests need probable cause. They can either be done on a warrant or without a warrant (in the latter case, in the federal system, a c

> Arrests need warrants. Arrests need probable cause. They can either be done on a warrant or without a warrant (in the latter case, in the federal system, a complaint must be filed and the arrested person must be brought before a magistrate for a hearing on probable cause within 72 hours after arrest.)