The shooter who killed five at the Fort Lauderdale airport in the U.S. state of Florida was officially charged with federal murder on Saturday.

The suspect, identified as Esteban Santiago, a 26-year-old Iraq war veteran, could face life sentence or death penalty if convicted, though his motive remains unclear.

"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," U.S. Attorney Wifredo Ferrer said.

The suspect was scheduled to make his first court appearance on Monday.

Santiago told investigators of the Federal Bureau of Investigation (FBI) that he bought a one-way ticket to the busy airport for the attack, local media reported.

Santiago went there "specifically to carry out this horrific attack," Miami FBI Special Agent George Piro told reporters earlier Saturday.

Authorities don't know why he chose his target and do not rule out terrorism.

"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," Piro said.

The suspect was not placed on the U.S. no-fly list and appears to have acted alone, authorities said.

Santiago flew into the airport at noon on Friday. Upon disembarking, he went to the baggage claim area, picked up his checked luggage, entered a bathroom, took out a pistol from his bag and loaded bullets. He then went out towards a baggage carousel and shot randomly, plunging the crowded terminal into chaos.

After firing 15 rounds, he dropped the handgun, lay on the ground facing down, spread eagle and waited for being arrested with no resistance, several witnessed said.

Aviation passengers in the United States are allowed to transport unloaded guns and ammunition in their checked baggage that are declared, according to the U.S. Transportation Security Administration (TSA).

The firearms must be kept in a secure container and declared to airline representatives at ticket counters, according to TSA regulations.

Five people were killed and six, instead of eight as earlier reported, were wounded in the attack, while about 40 people were taken to hospitals with bruises or broken bones suffered in the rushed evacuation after the rampage.

Since occurring at a usually-thought unlikely place, the shooting immediately raised alarm over U.S. aviation security, which has already been greatly tightened since 9/11 attacks.

The 26-year-old spent nine years of service in the National Guard including a 10-month tour of Iraq, the U.S. military confirmed. His last military assignment was in Alaska where he served as a member of the Alaska Army National Guard until August when he was discharged for unsatisfactory performance.

In November, Santiago 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.

His relatives said he had a history of mental health problems especially after returning from Iraq and received psychological treatment last year.  "Only thing I could tell you was when he came out of Iraq, he wasn't feeling too good," his uncle, Hernan Rivera, told The Record newspaper.

source: Xinhua