Behind the Scenes With the Air Marshals

July 8, 2004 -- One morning in May at New York City's JFK airport, John was trying to look like any other traveler. But John wasn't just a regular traveler. He and his team were planning to board a commercial airliner, fully armed and looking for trouble.

They weren't terrorists. Quite the opposite: John and his three partners are federal air marshals, the government's first defense against any crimes in the skies.

Since the Sept. 11, 2001, attacks, the air marshal operation has expanded exponentially. On that tragic day, there were only 33 of them.

Now there are thousands of federal air marshals — FAMs for short — and they fly more missions in one month than they did in the entire history of the program, before those attacks.

The program remains very secretive, in part to ensure its effectiveness. Nightline got an inside look at its operation — with the agreement that the marshals' last names be withheld and their faces be concealed.

Watch Nightline tonight at 11:35 p.m. ET.

A Simple Mission

At the airport, John identified himself to the ticket agent and got his assigned seat for a trip to Fort Lauderdale, Fla. Hours before the flight took off, he was already at work.

"I examine each and every person that I come in contact with," he told Nightline. "After two years of flying with the public, I have a good sense of what normal passenger activity is."

John, 38, has had 10 years of law enforcement experience with the National Park Service. His partners that day were Rick, 41, who has spent 17 years as a Dallas police officer; Marcus, 26, a former investigator for a New York prosecutor; and Annabelle, 26, formerly with the Immigration and Naturalization Service.

They all joined up shortly after the Sept. 11 attacks. Nearly all air marshals have a law enforcement or military background.

Annabelle outlined her responsibility succinctly: "To make sure that the plane gets down on the ground with everybody in it, including me!"

Alone in the Air

Much of a federal air marshal's training is designed to prevent a 9/11-style attack from ever happening again.