This booking photo provided by the Broward Sheriff's Office shows suspect Esteban Ruiz Santiago, 26, Saturday, January 7, 2017, in Fort Lauderdale

The Iraq war veteran accused of killing five travelers and wounding six others at a busy international airport in Florida was charged Saturday and could face the death penalty if convicted.

Esteban Santiago, 26, 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.

Santiago has been accused an act of violence at an international airport resulting in death - which carries a maximum punishment of execution - and weapons charges.

It has also been revealed that FBI agents took Santiago's gun off him when he went into an Alaska field office in November to say the government was controlling his mind.

But it was returned to him just a month later, and law enforcement will not reveal why. Sources told CNN he used the same weapon in the airport attack.

The alleged shooter was also left off all the no-fly lists and was allowed to check in his gun before Friday's attack.

This picture shows what may be the weapon that was used by the gunman in the shooting on Friday

A heavy police presence was at the Ft. Lauderdale-Hollywood International Airport after it re-opened Saturday, January 7, 2017

U.S Attorney Wifredo Ferrer formally announced Santiago's charges on Saturday.

They could result in capital punishment, but he would not confirm whether his office would be actively seeking the death penalty.

He said: 'Today's charges represent the gravity of the situation and reflect the commitment of federal, state and local law enforcement personnel to continually protect the community and prosecute those who target our residents and visitors,' .

Authorities said during a news conference that they had interviewed roughly 175 people, including a lengthy interrogation with the cooperative suspect, 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.

Santiago spoke to investigators for several hours after he opened fire with a Walther 9mm semi-automatic handgun that he appears to have legally checked on a flight from Alaska.

He had two magazines with him and emptied both of them, firing about 15 rounds, before he was arrested, the complaint 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,' FBI Agent George Piro said.

Passengers wait in the departure line at terminal 2 on Saturday after the airport reopened

George Piro, special agent in charge of the FBI's Miami Division speaks during a news conference at Fort Lauderdale-Hollywood International Airport Terminal

A hazmat crew cleans up baggage claim Terminal Two on Saturday, the day after multiple people were shot on Friday

A hazmat crew cleans up baggage claim Terminal Two on Saturday, the day after the mass shooting

A hazmat crew cleans up baggage claim Terminal Two on Saturday the day after multiple people were shot on Friday

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 U.S. government was controlling his mind and forcing him to watch Islamic State group videos, authorities said.

Dan Kovacs waits at the Fort Lauderdale-Hollywood International Airport, Saturday. Kovacs and his family were going through security when gunfire erupted yesterday. They had returned from a Caribbean cruise and were on their way home to Vancouver, Canada. In the mayhem after the shooting they lost their shoes, passports and ID's

Baggage claim area of Terminal 1 at Fort Lauderdale-Hollywood International Airport on Saturday the day after multiple people were shot at the airport

Passengers wait in line at Terminal 4 after the airport opened at 5:00 a.m. at Ft. Lauderdale-Hollywood International Airport, Saturday

Passengers sleep in Terminal 4 after the airport opened at 5:00 a.m.

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

On that day, 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 December 8, the gun was returned to Santiago.

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

The attack sent panicked witnesses running out of the terminal and spilling onto the tarmac, baggage in hand.

Law enforcement personnel tell people to take cover at Fort Lauderdale-Hollywood International Airport on Friday as a gunman opened fire

As chaos reined, people in a field at the perimeter of the airport were asked to raise their hands and verify their identity

People flee the area outside the Fort Lauderdale-Hollywood International airport on Friday

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.

Santiago flew into the airport from Anchorage, Alaska (with a layover in Minneapolis-St Paul) on Delta flight 2182 with a firearm as his only piece of checked luggage, in accordance with TSA regulations, authorities believe.

The 26-year-old, who was dressed in a Star Wars T-shirt, claimed his bag, went to the bathroom to load his handgun and then started shooting people dead, according to the county commissioner.

Witnesses said the gunman sprayed bullets around then lay down on the floor spread-eagled, awaiting arrest. They described the gunman as a 5'7'' male wearing a blue T-shirt.

Esteban Santiago, 26, the suspect in the deadly shooting at Fort Lauderdale-Hollywood International Airport, is transported to the Broward County Main Jail by authorities, Saturday

The suspect in the deadly Ft. Lauderdale airport shooting is transported to the Broward County Main Jail

Investigators said on Saturday morning they hadn't identified an altercation on the flight or at baggage claim that could have led to the shooting.

The suspect came to Fort Lauderdale-Hollywood airport 'specifically to carry out this horrific attack', FBI Special Agent In Charge George Piro said Saturday morning at a news conference.

'We have not identified any triggers that would have caused this attack,' he added. An early investigation revealed no particular reason that could have caused the suspect to pick the airport.

Terry Andres, of Virginia, and Olga Woltering, of Georgia, were among those who were killed. Andres, a 62-year-old grandfather, was at the airport with his wife to go on a vacation, while Woltering was scheduled to leave on a cruise from Florida on Saturday with her husband Ralph to celebrate his 90th birthday.

Esteban served in Iraq and walked into an FBI field office in November and said the government was trying to control his mind and making him watch ISIS videos

Michael Oehme, of Council Bluffs, Iowa, was identified Saturday as one of the five victims, according to local reports. Oehme was about to go on a cruise with his wife, Kari Oehme. She was shot in the shoulder but is expected to survive.

Witness 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.

Shooting victim Terry Andres and his wife Ann - The couple had flown to Florida to go on a Caribbean cruise. Both would have celebrated their birthdays on the trip

Shooting victim Olga Woltering (right), who lives in Atlanta, Georgia, was scheduled to leave on a cruise from Florida on Saturday with her husband Ralph to celebrate his 90th birthday, she was believed to be in her 80s

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.

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.

Michael Oehme, left, of Council Bluffs, Iowa, was one of the five victims killed in the Ft Lauderdale airport shooting. Oehme's wife Kari, right, was shot in the shoulder, but survived

'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.

Investigators did a background check and found no connection between Santiago and terror groups, USA Today wrote. They turned over the suspect to local authorities for a medical referral.

After that incident, Santiago started getting treatment for his mental health issues, sources said.

He was previously pictured giving a one-fingered salute, which is commonly used by Islamic State jihadists often before they embark on a suicide bombing.

Santiago was also contacted by the FBI after an employer back in Alaska raised concerns about certain things he had said, according to ABC News.

His aunt Maria Ruiz told NorthJersey.com that Santiago had returned from Iraq acting strangely but had seemed happy after the birth of his child in September last year.

But she said something happened to him about a month ago and he was hospitalized for two weeks. She did not have details of his condition.

'Like a month ago, it was like he lost his mind. He said he saw things,' she said.

Santiago's brother Bryan Santiago said he could have suffered a 'flashback' from his time in Iraq, despite never being diagnosed with PTSD, NBC reports.

Santiago had gone AWOL several times while serving in the Alaska National Guard, the Pentagon said. He had served from 2007 to 2016 in the Puerto Rico National Guard and in the Alaska National Guard, including a deployment to Iraq from 2010 to 2011.

The private first class and combat engineer received half a dozen medals before getting a general discharge for unsatisfactory performance in August last year.

Santiago had also been investigated as part of a child porn probe in 2011 or 2012, law enforcement told CBS News. Authorities seized three weapons and a computer but didn't file any charges, the network reported.

Santiago will make his first court appearance Monday.

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.

Despite his mental evaluation, US 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 high standard.