But Bryan Santiago said his brother didn't get the help he needed.
Esteban Santiago's aunt said her nephew talked about the destruction he witnessed. About the killing of children. Visions that haunted him.
"His mind was not right," Maria Ruiz Rivera told CNN in a phone interview from her home in New Jersey. "He seemed normal at times, but other times he seemed lost. He changed."
Bryan Santiago, who lives in Puerto Rico, said his brother asked authorities for help.
"And they did nothing. They had him hospitalized for four days, and then they let him go. How are you going to let someone leave a psychological center after four days when he is saying that he is hearing voices?"
Esteban Santiago is suspected of killing five people Friday at Florida's Fort Lauderdale-Hollywood International Airport
, authorities have said.
Relatives said he had been different since his tour in Iraq, where he was deployed with the Puerto Rico National Guard from April 2010 to February 2011.
'He had visions all the time'
"He talked about all the destruction and the killing of children. He had visions all the time," said Ruiz, speaking in Spanish during the interview.
Bryan Santiago said he believes the shooting rampage resulted from mental issues that appeared after Iraq.
Bryan Santiago, in an interview in Peñuelas, Puerto Rico, said he talked with people who know his brother and they told him he didn't get the treatment he needed.
The Santiago brothers hadn't talked lately, Bryan said.
Ruiz said she also lost contact with her nephew.
"He stopped calling," she said. "He wouldn't respond to my messages. I would call and text. He seemed distant."
On Friday, Ruiz said she heard her nephew's name during a TV news report on the Fort Lauderdale shooting.
"Who would have imagined that he could do something like this?" she said. "I don't say that because we're family. I say it because he wasn't like that."
Argument with girlfriend leads to charges
In January 2016, Esteban Santiago was arrested and charged with assault and criminal mischief after an argument with his girlfriend in Anchorage, Alaska, according to court documents that CNN obtained.
At the time, Santiago allegedly yelled at his girlfriend while she was in the bathroom, according to the complaint. He then broke down the bathroom door.
The woman told investigators that Santiago strangled her and struck her in the side of the head, the complaint said. Santiago left before police arrived.
Anchorage municipal prosecutor Seneca Theno said Santiago pleaded no contest to criminal mischief and assault charges. Under a deferred prosecution agreement, the charges would have been dismissed if he complied with the conditions. He was due back in court on March 28.
His record included two earlier minor offenses: no proof of insurance and a taillight violation in 2015.
Santiago was employed by an Anchorage security company, a law enforcement official said.
Ruiz said her nephew lived with his girlfriend and their child.
Several months ago, Santiago's strange behavior came to the attention of agents at the FBI's Anchorage office. The suspect allegedly told authorities at the time that an intelligence agency was telling him to watch ISIS videos, according to law enforcement officials.
Santiago brought a loaded pistol magazine into the FBI office, Anchorage Police Chief Chris Tolley said. He left his gun and child in the car. Police called the girlfriend to pick up the child and kept the pistol for safekeeping, Tolley said.
Marlin Ritzman, who heads the FBI office in Anchorage, said the FBI looked into Santiago's background and found no ties to terrorism.
The FBI asked police to take Santiago to get a mental health evaluation and Santiago voluntarily checked himself in.
"His erratic behavior concerned FBI agents," George Piro, the FBI's special agent in charge in Miami, said Saturday.
Anchorage police returned the gun when Santiago came to the police station in December to get it, Tolley said.
Investigators believe it was the same gun that was found at the scene of Friday's shooting, law enforcement sources told CNN.
Emerged from the airport bathroom shooting
Santiago flew to Florida on a Delta Air Lines flight from Alaska via Minnesota, officials said. He had declared his handgun in a firearms carrying case, a lieutenant with the Anchorage airport police said.
At the Fort Lauderdale airport, he picked up the carrying case at baggage claim, went into a bathroom stall and loaded a magazine, according to a federal criminal complain citing three crimes he is alleged to have committed.
Authorities are still trying to figure out why Santiago shot and killed five people.
Piro said Saturday that investigators "continue to look at the terrorism angle" as a possible motive.
"We have not ruled out anything," he said. "We continue to look at all avenues, all motives."
Santiago was cooperating with investigators, who had interviewed him for several hours, according to Piro. The interview concluded early Saturday.
Santiago is in federal custody and will appear Monday in court in Broward County, officials said.
The three federal charges have the death penalty as the maximum sentence, if Santiago is convicted.
It is unclear whether he has an attorney.
Discharge for unsatisfactory performance
Santiago joined the Puerto Rico National Guard in December 2007, said Lt. Col. Candis Olmstead of the Alaska Army National Guard.
After service in Iraq from April 2010 to February 2011, Santiago received the Iraq Campaign Medal with a campaign star, a combat-related honor, CNN's Barbara Starr reported.
He served in the US Army Reserve before joining the Alaska Army National Guard in November 2014, Olmstead said.
The suspect was later given a general discharge from the Alaska Army National Guard in August for unsatisfactory performance.
Santiago was not on the radar for possible terrorism ties, according to a law enforcement official and a Department of Homeland Security official.
He had no significant foreign travel that was ever flagged, another official said.