FLORIDA, United States (AP) — The Iraq war veteran accused of killing five travellers and wounding six others at a busy international airport in Florida appears to have travelled there specifically to carry out the attack, authorities said Saturday, but they don’t know why he chose his target and have not ruled out terrorism.

Authorities said during a news conference that they had interviewed roughly 175 people, including a lengthy interrogation with the cooperative suspect, 26-year-old Esteban Santiago, a former National Guard soldier from Alaska. Flights had resumed at the Fort Lauderdale airport after the bloodshed, though the terminal where the shooting happened remained closed.

FBI Agent George Piro said Santiago spoke to investigators for several hours after he opened fire with a 9mm semiautomatic handgun that he appears to have legally checked on a flight from Alaska.

“Indications are that he came here to carry out this horrific attack,” Piro said. “We have not identified any triggers that would have caused this attack. We’re pursuing all angles on what prompted him to carry out this horrific attack.”

Investigators are combing through social media and other information to determine Santiago’s motive, and it’s too early to say whether terrorism played a role, Piro said. In November, Santiago had walked into an FBI field office in Alaska saying the US Government was controlling his mind and forcing him to watch Islamic State group videos, a law enforcement official said.

Santiago had not been placed on the US no-fly list and appears to have acted alone, Piro said.

The attack sent panicked witnesses running out of the terminal and spilling onto the tarmac, baggage in hand. Others hid in bathroom stalls or crouched behind cars or anything else they could find as police and paramedics rushed in to help the wounded and establish whether there were any other gunmen.

Mark Lea, 53, had just flown in from Minnesota with his wife for a cruise when he heard three quick cracks, like a firecracker. Then came more cracks, and “I knew it was more than just a firecracker,” he said.

Making sure his wife was outside, Lea helped evacuate some older women who had fallen, he said. Then he saw the shooter.

“He was just kind of randomly shooting people,” he said. “If you were in his path, you were going to get shot. He was walking and shooting.”

Over the course of about 45 seconds, the shooter reloaded twice, he said. When he was out of bullets, he walked away, dropped the gun and lay face down, spread eagle on the floor, Lea said.

By that time, a deputy had arrived and grabbed the shooter; Lea put his foot on the gun to secure it.

Lea went to help the injured and a woman from Iowa asked about her husband, who she described. Lea saw a man who fit his description behind a row of chairs, motionless, shot in the head and lying in a pool of blood, he said. The man, Michael Oehme, was identified as one of the dead victims on Saturday.

Bruce Hugon, who had flown in from Indianapolis for a vacation, was at the baggage carousel when he heard four or five pops and saw everyone drop to the ground. He said a woman next to him tried to get up and was shot in the head.

“The guy must have been standing over me at one point. I could smell the gunpowder,” he said. “I thought I was about to feel a piercing pain or nothing at all because I would have been dead.”

Santiago had been discharged from the National Guard last year after being demoted for unsatisfactory performance. Bryan Santiago, said Saturday that his brother had requested psychological help but received little assistance. Esteban Santiago said in August that he was hearing voices, Bryan Santiago said. He said he told his brother then to seek help.

“How is it possible that the federal government knows, they hospitalise him for only four days, and then give him his weapon back?” Bryan Santiago said.

His mother declined to comment as she stood inside the screen door of the family home in Puerto Rico, wiping tears from her eyes. The only thing she said was that Esteban Santiago had been tremendously affected by seeing a bomb explode next to two of his friends when he was around 18 years old while serving in Iraq.

When Santiago spoke of mind control at the FBI office in November, agents questioned the agitated and disjointed man before calling police, a law enforcement official told The Associated Press. The official, who was not authorised to discuss the case and spoke on condition of anonymity, said Santiago was then taken for a mental health evaluation.

Piro, who is in charge of the Miami field office, said Santiago clearly indicated at the time that he was not intent on hurting anyone.

Santiago, who is in federal custody, will face federal charges and is expected to appear in court Monday, Piro said.

It is legal for airline passengers to travel with guns and ammunition as long as the firearms are put in a checked bag — not a carry-on — and are unloaded and locked in a hard-sided container. Guns must be declared to the airline at check-in.

Santiago arrived in Fort Lauderdale after taking off from Anchorage aboard a Delta flight Thursday night, checking only one piece of luggage — his gun, said Jesse Davis, police chief at the Anchorage airport.