Federal investigators said that the man suspected in the shooting at a south Florida airport went there “specifically" to carry out the shooting.
Authorities are still working to determine a motive for the shooting rampage that claimed the lives of at least five people and wounded six others. FBI officials said they have not ruled out terrorism as a possible motivation.
"Indications are he came here to carry out this horrific attack," said FBI Special Agent George Piro. "We have not identified any triggers that would have caused this attack but again it's very early in the investigation,"
“We have not ruled out anything,” he added. “We continue to look at all avenues, all motives.”
At a press conference later that afternoon in Anchorage, Alaska – where the suspect was living – FBI Special Agent Marlin Ritzman said there was no indication that Santiago worked with any other individuals prior to the attack.
Santiago had visited the Anchorage field office in November. He is said to have told agents that he was hearing voices in his head, that the government “controlled his mind” and “forced” him to watch videos encouraging him to join Isis.
When went to the office to speak with federal agents, he left his firearm and newborn child in the vehicle, according to Mr Ritzman.
The FBI looked into any potential contacts with terror groups, but later closed the investigation.
He was taken into custody by local police who took him to the hospital. He later voluntarily checked into a facility for mental health check.
Santiago's gun had been turned over to authorities while he underwent the psychological evaluation, but was later returned to him in December. Anchorage Police chief Christopher Tolley said it was not clear whether this was the same gun used in the Friday afternoon shooting.
Local authorities apprehended prime suspect Esteban Santiago, 26, after he allegedly opened fire in the Terminal 2 baggage claim area of Fort Lauderdale/Hollywood International Airport early Friday afternoon.
The suspect is unharmed and in federal custody.
New Jersey-born Santiago was reportedly on a flight from Alaska to Fort Lauderdale. When he landed at the Florida airport, he is believed to have retrieved his weapon from his checked bag, loaded it in the bathroom, and opened fire in the baggage terminal – allegedly shooting travellers at random.
Santiago had served in the National Guard and spent a year in Iraq in 2010. He later joined the Alaska National Guard and received an honourable discharge in August 2016, two years after joining.
The suspect’s brother, Bryan Santiago, told the Associated Press that he had been receiving psychological treatment in Alaska, where he was living.
Santiago is also facing prosecution for domestic violence charges. Last year, he allegedly threatened his girlfriend through a door, broke through it, and strangled her.
The assault case had been resolved, but he violated the terms of his release by showing up at his former partner’s house. Because the case did not lead to criminal charges against him, his right to own a firearm was not revoked.
Santiago will appear in a US federal court in Fort Lauderdale on Monday. He faces federal murder charges.
The Friday afternoon shooting sent the Florida airport into chaos as travellers ran out of the airport terminal, dozens of flights were grounded, and evacuees rushed for cover on the tarmac.
More than 40 people suffered injuries during the panic, including sprains and broken bones.
Florida Gov Rick Scott said he had been in contact with President-elect Donald Trump, but had not spoken to President Barack Obama in the aftermath of the shooting.
Mr Scott ordered flags be flown at half-mast at local and state buildings Saturday and Sunday to honour the victims of the attack.
On Saturday, the governor visited victims and family at the Broward Health Medical Centre. Many of the victims were still undergoing treatment and said to have been still fighting for their lives.
"If you lost somebody, it's just traumatic, it's just totally out of context," he said. "You never in your wildest dreams thought this would happen to you."
Three of the five victims have been identified as Terry Andres, 62, Michael Oehme, 57, and Olga Woltering, 84. All three victims flew to Fort Lauderdale to embark on cruise vacations.
Ms Woltering was with her 90-year-old husband, Ralph, who survived the shooting. Ms Woltering was originally from Ipswich in Suffolk, but lived in Atlanta.
Mr Oehme travelled from Iowa with his wife, 55, who survived after a bullet struck her in the shoulder during the attack.
Mr Andres had also flown to Fort Lauderdale from Norfolk, Virginia. He was with his wife at the time of the shooting, although she was not harmed.
Airport director Mark Gale announced that commercial flights resumed at 5am on Saturday. Terminal 2 is closed, with the exception of the upper level for Delta Arlines and Air Canada ticketing.