25 C.F.R. § 11.301 – Arrests.

(a) Arrest is the taking of a person into police custody in order that he or she may be held to answer for a criminal offense.
(b) No law enforcement officer shall arrest any person for a criminal offense except when:
1. (1) The officer shall have a warrant signed by a magistrate commanding the arrest of such person, or the officer knows for a certainty that such a warrant has been issued; or
2. (2) The offense shall occur in the presence of the arresting officer; or
3. (3) The officer shall have probable cause to believe that the person arrested has committed an offense.