Florida shooting suspect Esteban Santiago had told the FBI in November last year that he was being controlled by a U.S. intelligence agency that ordered him to watch videos made by the Islamic State.
Santiago, a 26-year old Iraq war veteran, was detained last Friday after he opened fire in a crowded baggage claim area at Fort Lauderdale's airport, killing five people, Reuters reported.
Broward County Commissioner Chip LaMarca said on Twitter that Santiago loaded his weapon in a restroom and came out firing. According to witnesses, he surrendered to the police after he ran out of ammunition.
Eight other people were injured by gunfire, and about three dozen were taken to the hospital for other injuries.
George Piro, a special agent in charge of the Federal Bureau of Investigation's office in Miami, said that Santiago appeared at the FBI office in Anchorage, Alaska last November behaving erratically and claiming that he was told to watch ISIS videos.
Santiago was deployed to Iraq from 2010 to 2011. His relatives have said that he suffered mental health problems when he came back from his deployment.
"Only thing I could tell you was when he came out of Iraq, he wasn't feeling too good," said his uncle, Hernan Rivera, according to Sydney Morning Herald.
His aunt, Ruiz Rivera, said that Santiago was hospitalized after his return. She stated that he seemed to get better and even became a father in September. However, his mental health problems got worse in December.
"They took him to the hospital, but they didn't tell me what for, but they had him in an isolated room because he was a little wrong in the head and he started to like hear things," she said.
Santiago's brother, Bryan, said that he should have been hospitalized for more than four days, given the seriousness of his claims.
"Four days for a guy who talked to the FBI (about) those things, that is a serious argument, you know. He goes to the FBI saying that he (was) hearing voices, that the CIA are saying that he needs to join ISIS," said Bryan.
According to a separate report from Reuters, police in Alaska took a handgun from Santiago after he went to the FBI office in Anchorage. It was returned to him after a month when a medical evaluation indicated that he was not mentally ill.
Santiago was charged with carrying out violence at an airport, using a firearm during a violent act, and killing with a firearm. He could potentially face the death penalty if he is convicted.