Fort Lauderdale shooting: US seeks death penalty as Esteban Santiago charged with massacre at Florida airport

Gunman's weapon was confiscated in November while he underwent a psychological evaluation, but was returned to him a month later

Esteban Santiago, 26, has been charged with an act of violence at an international airport resulting in death, and faces execution (Getty Images/ police handout)

The Iraq war veteran accused of opening fire at a Florida airport and killing five people could face the death penalty.

Esteban Santiago was charged with an act of violence at an international airport resulting in death on Saturday, which carries a maximum punishment of execution, as well as weapons offences.

The 26-year-old told investigators that he planned the attack, which injured several others, buying a one-way ticket to the Fort Lauderdale airport, a federal complaint said. Authorities do not know why he chose his target and have not ruled out terrorism.

Santiago, who was honourably discharged from the Alaskan National Guard last August, had recently received psychiatric treatment, his brother said.

US Attorney Wifredo Ferrer 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 told journalists during a news conference that they had interviewed roughly 175 people, including a lengthy interrogation with the "co-operative" suspect.

Santiago reportedly 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.

At a press conference on Saturday afternoon in the suspect's hometown of Anchorage in Alaska, FBI agents said there was no indication that Santiago worked with any other individuals prior to the attack.

“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,” agent George Piro said.

Investigators are combing through social media and other information to determine Santiago's motive, and it is too early to say whether terrorism played a role, Mr Piro added.

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 Isis videos, said special agent Marlin Ritzman.

He left his gun and newborn child in the vehicle, according to Mr Ritzman.

He was taken into custody by local police who took him to the hospital and later voluntarily checked into a facility for mental health treatment.

Santiago's gun was turned over to authorities while he underwent the psychological evaluation, but was later returned to him in December.

The FBI looked into any potential contacts with terror groups, but later closed the investigation.

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

Authorities would not confirm if the gun confiscated and returned to Santiago was the same one used in the attack.

Additional reporting by Associated Press