People on the airport ramp area near terminals 1 and 2 are seen following a shooting incident at Fort Lauderdale-Hollywood International Airport in Fort Lauderdale, Florida, U.S. January 6, 2017. (Xinhua/REUTERS)

WASHINGTON, Jan. 7 (Xinhua) -- The Iraq war veteran accused of killing five people at the Fort Lauderdale airport, the U.S. state of Florida, "came here specifically to carry out this horrific attack," authorities said on Saturday.

The 26-year-old suspect, identified as Esteban Santiago, cooperated with investigators during an interview that lasted several hours overnight, George Piro, special agent in charge of the Federal Bureau of Investigation (FBI)'s office in Miami, told reporters.

"We have not identified any triggers that would have caused this attack," Piro said, as investigators were probing whether mental illness played a role in the latest shooting rampage.

The FBI has not ruled out terrorism, Piro said, noting it's too early to draw a conclusion. "We continue to look at all avenues, all motives."

Esteban Santiago, is shown in this booking photo provided by the Broward County Sheriff's Office in Fort Lauderdale, Florida, January 7, 2017. (Courtesy Broward County Sheriff's Office/Handout via REUTERS)

The suspect flew into the airport at noon time on Friday. Upon disembarking, he went to the baggage claim, 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, sending the crowded terminal into chaos.

After a round of shooting, he dropped the handgun, lay ground, faced down, spread eagle and waited for being arrested with no resistance, several witnesses said.

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

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

Five people were killed and eight others 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.

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

The suspect, Santiago, spent nine years of service in the National Guard which included one 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.

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.