Special Agent

In the United States, a special agent is usually a criminal investigator or detective for a federal, state, or county government who primarily serves in investigatory roles. Within the United States' federal law enforcement system, dozens of federal agencies employ federal law enforcement officers, each with different criteria pertaining to the use of the titles "Special Agent" versus "Agent". In intelligence usage, agent refers to one who is recruited, trained, controlled and employed to obtain and report information.[1]
In general, some, but not all, agents are federal law enforcement officers, and hold either arrest authority or the right to conduct minor criminal/non-criminal investigations. In some agencies, however, an agent can have both arrest and minor criminal/non-criminal investigatory authority, yet still have no authority to conduct major criminal investigations. On the other hand, nearly all special agents are federal law enforcement officers, are distinctly empowered to conduct both major and minor criminal investigations, and hold arrest authority. Most special agents are authorized to carry firearms both on and off-duty, whereas only some agents are authorized to do so. The title of special agent is almost exclusively used in federal law enforcement (United States) for federal criminal investigators.