And that is what he was - butunlike every other G-man, he went on to become bureau boss.
After the tragedy of Oklahoma City, President Bill Clinton may make the speeches, the Attorney General, Janet Reno, may be the cabinet face of law enforcement. But the man in real charge of the investigation is Louis Freeh.
A mere 43 when picked as FBI director in July 1993, he has wrought a small revolution in a 20,000-strong bureaucracy hardly changed since the heyday of J Edgar Hoover. His rise was meteoric. He joined in New York in 1975 and served at head office in Washington before transferring back to New York as a junior agent. He was put to work on Unirac, a sprawling investigation into links between organised crime and the East Coast labour movement. It yielded 125 convictions.
After six years, the star G-man resigned to become a federal prosecutor. He helped to crack the "Pizza Connection", named after restaurants the Mafia used as heroin-smuggling fronts. President George Bush named him a federal district judge in 1991. Two years later, on the advice of a former White House counsel, Bernard Nussbaum, President Clinton picked him as FBI head.
Even for an established Washington figure, the task would have been daunting. When Mr Freeh arrived, the Bureau was in a wretched state. Apocalypse at Waco was fresh in the memory and his predecessor, William Sessions, had been fired. The FBI building was ripe for a shake-up. A shake- up it got.
Hundreds of Washington desk jobs were cut, occupants being reassigned to field offices. He acted to end turf wars with other federal agencies and gave the FBI an international focus, opening a Moscow office in 1994 and later this year, a Peking one.
The upheavals have not pleased everyone. Cronyism accusations are rife among an old guard that resents his naming outsiders for key jobs. More serious are fears that central bureaucracy cuts could damage the Bureau's ability to support and co-ordinate work in the field. Oklahoma will be a decisive test.