FORT LAUDERDALE, Fla. — Authorities took a gun away from New Jersey-born Iraq war veteran Esteban Santiago weeks before he allegedly killed five travelers and wounding six others at a busy international airport in Florida.

But the gun was returned to him because he hadn't been judged mentally ill — even though he'd been subjected to a mental health evaluation.

Esteban Santiago, 26, has been charged with an act of violence at an international airport resulting in death — which carries a maximum punishment of execution — and weapons charges.

Santiago told investigators that he planned the attack, buying a one-way ticket to the Fort Lauderdale airport, a federal complaint said. Authorities 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 a cooperative Santiago, who is 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 semi-automatic 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.

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.

Said government was controlling his mind

In November, Santiago had walked into an FBI field office in Alaska saying the U.S. government was controlling his mind and forcing him to watch Islamic State group videos, authorities said.

"He was a walk-in complaint. This is something that happens at FBI offices around the country every day," FBI agent Marlin Ritzman said.

Santiago had a loaded magazine on him, but had left a gun in his vehicle, along with his newborn child, authorities said. Officers seized the weapon and local officers took him to get a mental health evaluation. His girlfriend picked up the child.

On Dec. 8, the gun was returned to Santiago. Authorities wouldn't say if it was the same gun used in the airport attack.

U.S. Attorney Karen Loeffler said Santiago would have been able to legally possess a gun because he had not been judged mentally ill, which is a higher standard than having an evaluation.

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

Santiago's service in the National Guard

Bryan Santiago speaks about his brother Esteban. (AP Photo/Danica Coto)

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.

"How is it possible that the federal government knows, they hospitalize 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.

Santiago, who is in federal custody with no bail, 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.

New Jersey roots

Authorities have said Santiago was born in New Jersey

“He lost his mind,” his aunt, Maria Ruiz, a Union City resident, is quoted by NJ.com as saying in Spanish.

His aunt told NorthJersey.com that her nephew “said he saw things.”

“Like a month ago, it was like he lost his mind,” she’s quoted as saying.

In recent years, Santiago had been living in Anchorage, Alaska, Bryan Santiago, told The Associated Press from Puerto Rico.

— Based on Associated Press reports

Copyright 2017 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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