The emergency management worker in Hawaii responsible for sending out a mistaken alert last month warning of an incoming missile said Friday that he was convinced the threat was real and was 100 percent sure at the time that he was doing the right thing.

I heard, This is not a drill. ... Im really not to blame in this. It was a system failure. I did what I was trained to do , the man told NBC News in his first media interview.

He agreed to talk about the incident on the condition that his identity not be revealed because of death threats he has received. His face was in darkness as he spoke. He was fired from his job at the Hawaii Emergency Management Agency last month.

The Jan. 13 alert, sent out on cellphones to over 1 million people , caused panic among residents, whose fears were heightened by recent threats of a nuclear attack on the U.S. by North Korea.

A second alert notifying residents that the warning had been sent in error wasnt transmitted for 38 minutes .

It was incredibly difficult for me, very emotional, the man told NBC. He said when he realized he had made a mistake he just wanted to crawl under a rock .

He added: I feel very badly for whats happened the panic, the stress people felt, all the hurt and pain. I feel that myself ... . Its been very difficult.

He believes we werent prepared to send out missile notifications. I think the military should do that, he added.

The former employee was a source of concern ... for over 10 years , according to a report last month by Brig. Gen. Bruce Oliveira of the Hawaii National Guard, who conducted an internal investigation for the emergency agency. The worker had a history of confusing drill and real-world events, including a drill for a fire and a tsunami warning, Oliveira said at a news conference earlier this week, NBC reported.

A recorded missile drill played for workers began and ended with the phrase exercise, exercise, exercise, according to a federal probe, though the worker said he didnt hear those words. The practice warning, however, also included the words this is not a drill, investigators found. Other workers understood that the drill was just an exercise, according to investigators.

The fired worker refused to cooperate with federal or local investigations , the Federal Communications Commission and a state emergency official said late last month.

A preliminary report from the FCC found that the drill was run without sufficient supervision and that there were no procedures in place to prevent a single person from mistakenly sending a missile alert from the state.