If there is probable cause to believe that a person committed a crime, he or she may be arrested based on a warrant previously issued by a Court or, under certain circumstances, without a warrant. However, not all brief detentions by federal agents or local police are considered arrests. Factors in determining whether someone was "under arrest" include: length of detention, transportation to another location (such as the police station), restraint on ability to leave, handcuffing, amount of force employed and number of agents involved in the restraint of movement.

Regardless of whether individuals are formally "under arrest," or merely detained, they retain their constitutional rights, including their right to counsel and their right not to incriminate themselves. Remember that under most circumstances, even when one has not been advised of one's rights, anything one says may be used against him or her. Be cautious of any promises or representations regarding leniency or immunity made by federal agents because only the federal prosecutors have the legal authority to make legally binding promises regarding prosecution.