(1) CRIME IN THE OFFICER'S PRESENCE: an officer can always arrest a person for a crime committed in the officer's presence, no matter how minor the crime. Atwater v. City of Lago Vista, 532 U.S. 318 (2001)
(2) ARREST WARRANT: with an arrest warrant, the judge has already determined that there is probable cause for an arrest;
(3) INFORMANTS: the officer must have a basis for the truthfulness of the informant's statement. Illinois v. Gates U.S. 213 (1983);
CRIME OBSERVED BY ANOTHER OFFICER
(4) CRIME OBSERVED BY ANOTHER OFFICER: an officer may rely on information received from a fellow officer in determining probable cause to arrest.