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FORT LAUDERDALE (CBSMiami) – The suspected gunman in a deadly attack at Fort Lauderdale-Hollywood International Airport “lost his mind” after coming back home from a one-year tour in Iraq, family members told the media.

Investigators are now looking into what may have set off 26-year-old Esteban Santiago Ruiz into a shooting rampage that left five dead and six others wounded.

“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 Bergen Record newspaper, as reported by The Associated Press.

Bryan Santiago, the suspect’s brother, said Esteban’s girlfriend had recently called the family to alert them to his treatment. Though, she didn’t provide many details.

“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.”

On Friday, Esteban Santiago took a flight from Alaska to Florida with a lay over stop in Minnesota. Somewhere along the way, he got into an argument with someone, officials said.

According to Broward Commissioner Chip LaMarca, Santiago arrived in Fort Lauderdale with a gun that he checked in.

“He claimed his bag and took the gun from baggage and went into the bathroom to load it. Came out shooting people in baggage claim,” LaMarca said.

Passengers are legally allowed to travel with guns and ammunition as long as the firearms are unloaded, secured in a lock box and not brought on board the plane as a carry-on. They must be declared to the airline at check-in.

Earlier reports claimed Santiago came in on a flight from Canada. On the company’s Twitter account, Air Canada confirmed that no one by that name was on their flight.

Air Canada flights arrive to Terminal 2, where the shooting took place.

We confirm we have no record of a passenger by the name Esteban Santiago, or checked guns, on any of our flights to Fort Lauderdale #FLL 5/5 — Air Canada (@AirCanada) January 6, 2017

It was later determined that Santiago-Ruiz was on a Delta Air Lines flight.

Santiago was born to Puerto Rican parents in New Jersey and recently became a father of a baby boy.

His aunt, according to nj.com, said after a tour of duty in Iraq, he “lost his mind” and was hospitalized at one point for mental health issues.

The Pentagon said he went AWOL several times as a specialist during a stint with the Alaska National Guard and was demoted to private first class, the Associated Press reported. He was given a general discharge, which is lower than an honorable discharge.

The FBI said they were trying to confirm where he served.

In November 2016, he walked into an FBI office in Anchorage claiming that he was being forced to fight for ISIS and was sent to a psychiatric hospital.

FBI spokesman George Piro confirmed he was evaluated by the FBI while living in Alaska.

“He did go to our office in Anchorage, but he did not want to commit harm,” the agent said. “He voluntarily entered our office and was interviewed by agents of the office. He was turned over to local custody and then taken to a local hospital.”

So far, Santiago has no known connection to terrorism, with the exception of this photo showing him wearing an Arabic keffiyeh and pointing a finger in the air – a symbol ISIL militants use.

However, the FBI has not ruled out anything.

“We have begun the difficult task of processing the crime scene,” said the FBI’s George Piro. “We have not ruled out terrorism and we will be perusing every angle to try to determine a motive behind this attack.”

About five years ago, he was investigated by Homeland Security Investigations for child porn. Three weapons and a computer were seized, but there was not enough evidence to prosecute, according to law enforcement sources.

Santiago also has a record for minor traffic violations and was evicted in 2015 for not paying rent.

He had been living in a modest apartment in Anchorage. His neighbor was in disbelief.

“He was always pleasant. Didn’t show any signs of no threats. Just always pleasant,” said Perette Carter. “He used to play with my niece and nephews. My brother talked to him. Always pleasant.”

Police were able to apprehend the alleged gunman without having to fire their own weapons when he apparently ran out of bullets. Witnesses said he threw down his firearm and laid on the floor with his hands and feet spread out wide.

He wasn’t hurt in the incident and no one else was taken into custody.

Written by James Amalino, CBSMiami.