Investigators were still trying to figure out whether an 80-second airport shooting rampage, allegedly carried out by a gunman more than 4,000 miles from home, was driven by a terror motive or mental illness, authorities said.

A day after five were killed at the Fort Lauderdale-Hollywood International Airport, agents had interviewed more than 100 people, including the suspected shooter, Esteban Santiago, 26, who'd surrendered by dropping onto the floor near a baggage area.

Authorities and family members portray Santiago, a U.S. citizen with ties to New Jersey and Puerto Rico, as an Iraq veteran who struggled with mental health issues and who, two months earlier, had walked into an Alaska FBI field office and told agents his mind was being controlled, complaining that the government was forcing him to watch Islamic State videos.

Esteban Santiago, 26, the suspect in the deadly shooting at Fort Lauderdale-Hollywood International Airport, is transported to the Broward County Main Jail. Photo / AP
Esteban Santiago, 26, the suspect in the deadly shooting at Fort Lauderdale-Hollywood International Airport, is transported to the Broward County Main Jail. Photo / AP

Investigators are scouring Santiago's electronics and digital media, a law enforcement official familiar with the case said, trying to determine whether he had any real contact with Islamic State sympathisers and whether that motivated him to carry out the shooting.

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"We have not ruled out anything," George Piro, the FBI special agent in charge of the bureau's Miami division, said at a Saturday morning briefing. "We continue to look at all avenues, all motives for this attack. And we continue to look at the terrorism aspect as a motive."

The bloody rampage sent people scrambling through the terminals and across the airfield at one of the country's busiest airports, shutting down all flights for hours as paramedics and federal and local law enforcement officers flooded the scene. Six were injured in the shooting, and dozens more were also injured in the chaos that followed the shooting.

An unidentified couple from Chicago react after evacuating from Terminal 1 following the shooting. Photo / AP
An unidentified couple from Chicago react after evacuating from Terminal 1 following the shooting. Photo / AP

Santiago was placed in federal custody Saturday morning following a lengthy interview by Broward County sheriff's deputies and FBI agents. He will face federal charges, officials said.

The FBI is leading a sprawling investigation that spans from Florida to Alaska. Names of victims have not yet been released, because not all families have been notified.

Santiago is believed to have lived most recently in Alaska with a girlfriend and young child. In his November encounter with the FBI, Santiago clearly indicated he was not intent on hurting anyone, Piro said. But what another federal official called incoherent and erratic statements led agents to ask local police to take him for a mental health evaluation. The FBI interviewed his family members, conducted database reviews and interagency checks, and ultimately closed what it termed an "assessment" of Santiago.

Law enforcement personnel tell people to take cover. Photo / AP
Law enforcement personnel tell people to take cover. Photo / AP

Santiago arrived in Fort Lauderdale on Friday after flying from Anchorage, with a layover in Minneapolis. He travelled alone and checked a single bag - one that contained his firearm, said Jesse Davis, chief of police at Ted Stevens International Airport in Anchorage, where passengers routinely check their weapons. "We're a big hunting state, so we get quite a lot of that," Davis said.

"Everything appeared normal," Davis said. Santiago checked in for his Delta flight more than four hours early, which was unusual, Davis said, but "didn't call attention to himself at all."

In Fort Lauderdale, at the Terminal 2 baggage claim, Santiago picked up his bag from the carousel, went to the bathroom, and loaded his 9mm handgun, federal officials said. When he came out, he allegedly began firing.

Law enforcement personnel arrive in an armored car. Photo / AP
Law enforcement personnel arrive in an armored car. Photo / AP

Travellers are allowed to bring firearms with them onto flights as long as the guns are unloaded, locked in a hard-sided container and in checked baggage, according to the Transportation Security Administration. Ammunition can be brought onto flights but also must be placed in checked baggage.

Mario Andrade, a driver from Carey Limousine, was waiting for his customer, former George W. Bush White House press secretary Ari Fleischer, near the bottom of the escalator in the Delta baggage area of Terminal 2. He was holding a sign with Fleischer's last name and talking on the phone with another driver. Fleischer's 12:15 p.m. flight was late and it was nearly 1 p.m.

Suddenly, he heard gunfire.

People run on the tarmac during the shooting. Photo / AP
People run on the tarmac during the shooting. Photo / AP

"It was very fast, like tat-tat-tat-tat-tat-tat," Andrade said. "I said, Oh my God, someone is shooting!"

He immediately dropped to the floor. People were running and he heard screaming all around him.

Andrade looked up and saw a man in a blue shirt who had a gun in his hand. The gunman began walking slowly toward him. He said the gunman had a "surprised look" on his face, "like, Oh my God, what happened?"

People stand on the tarmac at the Fort Lauderdale-Hollywood International Airport after a shooter opened fire inside a terminal of the airport. Photo / AP
People stand on the tarmac at the Fort Lauderdale-Hollywood International Airport after a shooter opened fire inside a terminal of the airport. Photo / AP

Relatives of the alleged shooter told news outlets that Santiago had a history of mental health problems, including some that followed his military service in Iraq with the Puerto Rico National Guard.

"Only thing I could tell you was when he came out of Iraq, he wasn't feeling too good," his uncle, Hernan Rivera, told Newark's Star-Ledger newspaper.

His aunt told the newspaper he was hospitalised after returning from Iraq. "He lost his mind," Ruiz Rivera said in Spanish.

A shooting victim arrives at Broward Health Trauma Centre. Photo / AP
A shooting victim arrives at Broward Health Trauma Centre. Photo / AP

He had seemed to get the help he needed, and became a father in September, she told Noticias Telemundo. But his mental health issues resurfaced 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.

The airport reopened Saturday morning for flights, officials said, though they warned that some flights were cancelled or rerouted in the wake of Friday's violence. Some Travellers were also being directed to South Florida's other two major airports in Miami and West Palm Beach.