US prosecutors have filed charges against the Florida airport shooting suspect that could bring the death penalty if he is convicted.
A criminal complaint filed on Saturday by the Miami US attorney's office accuses 26-year-old Esteban Santiago of an act of violence at an international airport resulting in death. The punishment is execution or any prison sentence up to life.
Prosecutors also charged Santiago with two firearms offences.
Santiago is accused of fatally shooting five people and wounding six others Friday at a Fort Lauderdale-Hollywood International Airport baggage claim.
The FBI says Santiago travelled from Alaska to Fort Lauderdale specifically to carry out the shooting.
Santiago, an Iraq war veteran, is being held without bail. He is scheduled to make his first court appearance on Monday.
"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," US Attorney Wifredo Ferrer said.
Authorities said during a news conference that they had interviewed roughly 175 people, including a lengthy interrogation with the co-operative suspect, a former National Guard soldier from Alaska. Flights had resumed at the Fort Lauderdale airport after the bloodshed, though the terminal where Friday's 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.
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, Mr Piro said.
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 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.
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. Authorities wouldn't say if it was the same gun used in the airport attack.
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 higher standard than having an evaluation.
Santiago had not been placed on the US no-fly list and appears to have acted alone, authorities said.
He had been discharged from the National Guard last year after being demoted for unsatisfactory performance. Bryan Santiago said his brother had requested psychological help but received little assistance.