The man arrested at the Atlanta airport after his family reported he had threatened to shoot up the terminal is pleading not guilty to federal charges.

Billy Joe Cagle, 49, appeared in court on Friday for a hearing where he made his plea.

Atlanta police arrested Cagle in Hartsfield-Jackson Atlanta International Airport's South Terminal on Oct. 20, after his family alerted the Cartersville Police Department that he threatened to "shoot up" the airport on a FaceTime call while driving, abruptly ending the call after saying, "I'm at the airport, and I'm gonna go rat-a-tat-tat," prosecutors alleged.

Cagle arrived at the airport in a Chevrolet pickup truck that was parked outside the doors to the terminal. When police went to the vehicle, they found an AR-15 with 27 rounds of ammunition. The FBI says they are working to find out how Cagle obtained the weapon.

Officer Myesha Banks, who has been with the Atlanta Police Department for nearly three years and at the airport for about two years, identified and arrested Cagle.

"I did go into tunnel vision and all of my skills and everything I learned just came as one, and that's when I just went into straight police mode," Banks said.

Police estimate that more than 20 people could have been killed if officers hadn't been alerted in time.

A day after his arrest, Federal prosecutors said that they had charged Cagle with attempted violence at an international airport, interstate communications containing threats, and being a felon in possession of a firearm. Locally, he was charged with making terroristic threats, criminal attempt to commit aggravated assault, possession of a firearm during the commission of a felony, and possession of a firearm by a felon.

"Cagle senselessly threatened to do heinous violence to innocent travelers, at the world's busiest airport, with a high-powered weapon that he had no legal right to possess," said U.S. Attorney Theodore S. Hertzberg. "Thanks to the vigilance of other citizens and the quick action of law enforcement, a horrible tragedy was averted."

Speaking after Cagle made his plea, his attorneys argued that their client was having a mental crisis at the time of his arrest.

The Cartersville man remains in federal custody after a judge denied him bond in late October.

The Associated Press contributed to this report.