The suspected killer in the Ft. Lauderdale rampage, 26-year-old Esteban Santiago, was charged on Saturday with performing an act of violence at an airport, which could earn him the death penalty if he is convicted.
Santiago was charged with an act of violence at an international airport resulting in death and weapons charges.
Earlier, the FBI announced that Santiago apparently traveled to the airport for the purpose of carrying out the bloody rampage.
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.
Terrorism may have been a "potential motivation" for the attack on Friday that killed five people, Special Agent in Charge George Piro said during a news conference.
Later in the afternoon, police in Alaska said they had returned a handgun to the Florida airport shooting suspect which was temporarily taken from him when he underwent a mental evaluation late last year, according to a Reuters report.
Anchorage Police Chief Christopher Tolley said it was not immediately clear if it was the same gun used in Friday's deadly rampage. Officials told a news conference the gun was returned to the suspect because the Iraq war veteran had not committed a crime.
Why the gunman may have chosen South Florida was unclear. He had no clear connection to the state aside from relatives in the Naples area, a two-hour drive away, the Sun Sentinel reported.
The suspected shooter had a history of mental health problems -- some of which followed his military service in Iraq -- and was receiving psychological treatment at his home in Alaska, his relatives said.
FBI investigators questioned Santiago for hours. Piro said investigators were scouring the 26-year-old suspect's social media footprint and looking into where he'd traveled before.
Santiago was not on any no-fly list, according to the FBI. He allegedly carried out the attack with a 9 mm semi-automatic handgun, Piro added.
Broward County Sheriff Scott Israel said six people were wounded in the attack -- not eight, as officials had said Friday. Three were in the intensive care unit and three were in good condition, Israel told reporters.
"Only thing I could tell you was when he came out of Iraq, he wasn't feeling too good," Santiago's uncle, Hernan Rivera, told The Record newspaper.
Santiago deployed in 2010 as part of the Puerto Rico National Guard, spending a year with an engineering battalion, according to Guard spokesman Maj. Paul Dahlen.
In recent years, Santiago -- a new dad, family said -- had been living in Anchorage, Alaska, his brother, Bryan Santiago, told The Associated Press from Puerto Rico. Bryan Santiago said his brother's girlfriend had recently called the family to alert them to his treatment.
In November, Esteban told FBI agents in Alaska that the government was controlling his mind and was forcing him to watch Islamic State group videos, a law enforcement official said. The official was not authorized to discuss an ongoing investigation by name and spoke Friday on condition of anonymity.
The FBI agents notified the police after the interview with Esteban Santiago, who took him in for a mental health evaluation.
Bryan Santiago said his brother never spoke to him directly about his medical issues.
"We have not talked for the past three weeks," Bryan Santiago said. "That's a bit unusual ... I'm in shock. He was a serious person ... He was a normal person."
Esteban Santiago was born in New Jersey but moved to Puerto Rico when he was 2, his brother said. He grew up in the southern coastal town of Penuelas before joining the Guard in 2007.
Former neighbor Ursula Candelario recalled seeing Esteban Santiago grow up and said people used to salute him after he joined the Guard. "He was very peaceful, very educated, very serious," she said. "We're in shock. I couldn't believe it," said Candelario.
While in Iraq, Santiago cleared roads of improvised explosive devices and at least two members of his company were killed, spokesman Lt. Col. Candis Olmstead told The New York Times. He was awarded a Meritorious Unit Commendation.
Since returning from Iraq, Santiago served in the Army Reserves and the Alaska National Guard in Anchorage, Olmstead told the AP. He was serving as a combat engineer in the Guard before his discharge for "unsatisfactory performance," said Lt. Col. Candis Olmstead, a spokeswoman. His military rank upon discharge was E3, private 1st class, and he worked one weekend a month with an additional 15 days of training yearly, Olmstead said.
She would not elaborate on his discharge, but the Pentagon said he went AWOL several times and was demoted and discharged.
Still, he'd had some successes during his military career, being awarded a number of medals and commendations including the Iraq Campaign Medal and the Global War on Terrorism Service Medal.
His uncle and aunt in New Jersey were trying to make sense of what they were hearing about Santiago after his arrest at the Fort Lauderdale airport. FBI agents arrived at their house to question them, and reporters swarmed around.
Maria Ruiz told The Record that her nephew had recently become a father to a son and was struggling.
"It was like he lost his mind," she said in Spanish of his return from Iraq. "He said he saw things."
Santiago was flying from Anchorage on a Delta flight and had checked only one piece of luggage, which contained the gun.
Santiago was charged in a domestic violence case in January 2016, damaging a door when he forced his way into a bathroom at his girlfriend's Anchorage home. The woman told officers he yelled at her to leave, choked her and smacked her on the side of the head, according to charging documents.
A month later municipal prosecutors said he violated the conditions of his release when officers found him at her home during a routine check. He told police he had lived there since he was released from custody the previous month. His Anchorage attorney, Max Holmquist, declined to discuss his client.
Law enforcement officers were at the girlfriend's home Friday afternoon, and officers guarding the property outside told a reporter who approached the home to step away.
Senator-elect Nelson Cruz, who knew the family and represents the town where they live in Puerto Rico, said he had been talking regularly with Bryan Santiago since the shooting.
"They're very humble and very Christian people," Cruz said of Esteban Santiago's brother and mother. "They want to tell the families of the victims that they're extremely saddened and extremely upset by what happened."
The Associated Press contributed to this report.