Correction: This article has been updated to correct Esteban Ruiz Santiago's name, and to correct the number of shooting victims.

UNION CITY -- The suspect in the Fort Lauderdale shooting was a U.S. military veteran who "lost his mind" after a tour of duty in Iraq, his aunt said Friday.

Maria Ruiz Rivera, of Union City, said she was told by relatives in Florida that the suspected shooter who killed at least five people at the Fort Lauderdale airport Friday was her nephew, Esteban Ruiz Santiago.

Agents who identified themselves as being from the FBI arrived at the family's Union City apartment Friday afternoon to question the aunt and uncle about their nephew, the family said. They were seen leaving shortly before 6 p.m.

Ruiz Rivera said relatives in Florida were also contacted by law enforcement officials Friday afternoon.

Santiago, who was born in New Jersey, was living in Alaska and has a newborn baby boy, his aunt told NJ Advance Media. He appeared to be doing well and was working a security job in recent months, she said.

But he was hospitalized for mental health issues after returning from a year-long tour in Iraq about five years ago, his aunt said.

"He lost his mind," Ruiz Rivera said in Spanish.

Maria Ruiz Rivera, of Union City, Santiago-Ruiz's aunt, shows a picture of Esteban on Facebook. (Fausto Giovanny Pinto | NJ Advance Media for NJ.com)

Her husband, Hernan Rivera, said he was unsure why Santiago might have opened fire in the baggage claim area of the Florida airport.

"No idea. Only thing I could tell you was when he came out of Iraq, he wasn't feeling too good," Hernan Rivera said.

Santiago's brother in Puerto Rico said the suspected shooter had been recently receiving psychological treatment while living in Alaska.

Bryan Santiago said his family got a call in recent months from Esteban Santiago's girlfriend alerting them to the situation. But Bryan Santiago said he did not know what his brother was being treated for and they never spoke about it by phone.

Authorities in Florida have not identified the suspect arrested after killing five and injuring six in a shooting at the Fort Lauderdale airport. The suspect was taken into custody without incident and appeared to act alone.

A tweet from Broward Commisioner Chip LaMarca said he was told the shooter arrived in Fort Lauderdale as a passenger on a flight from Canada with a gun checked in his bag.

He retrieved the checked bag at baggage claim, went to the bathroom to take out the gun, then opened fire in the baggage claim area, LaMarca said.

CBS News reported Santiago was known to the FBI. In November, he walked into the FBI office in Anchorage and told agents he was being forced to fight for ISIS, sources told CBS.

NEW: In Nov. 2016, FLL suspect walked into FBI office in Anchorage, claiming he was being forced to fight for ISIS, sources tell CBS News. — CBS News (@CBSNews) January 6, 2017

Santiago, 26, was born in New Jersey to parents who were originally from Puerto Rico, his aunt and uncle in Union City said. He lived in New Jersey until age 2 or 3, when his family moved back to Puerto Rico.

Santiago grew up in the southern coastal town of Penuelas in Puerto Rico, said his brother, Bryan Santiago. He joined Puerto Rico's National Guard.

He was deployed to Iraq in 2010 and spent a year there with the 130th Engineer Battalion, the 1013th engineer company out of Aguadilla, according to Puerto Rico National Guard spokesman Maj. Paul Dahlen.

After his tour, he was hospitalized for mental problems, then went back to Puerto Rico, where his father was ill and eventually died, said Ruiz Rivera, his aunt.

While in Puerto Rico, Santiago was in therapy for his mental problems, his uncle said.

The Iraq War veteran eventually made his way to Alaska, where he fathered a baby born in September.

A spokeswoman for the Alaska Army National Guard said Santiago joined the Guard there in November 2014, but general discharge from the Alaska Army National Guard last year for unsatisfactory performance. Lt. Col. Candis Olmstead did not release details about the discharge, which was in August 2016.

According to an Army record of his service, Santiago did receive a number of commendations, including a Good Conduct Medal, The New York Times reported.

People stand on the tarmac at the Fort Lauderdale-Hollywood International Airport after a shooter opened fire inside a terminal of the airport, killing several people and wounding others before being taken into custody (Al Diaz | Miami Herald via AP)

Ruiz Rivera said the last time she saw her nephew was about four years ago when he spent a week with his family in Union City over Christmas.

She last spoke to her nephew after his son's birth. He seemed fine, she said.

However, when she texted him on Christmas Eve, he did not return the message, Ruiz Rivera said.

The couple spoke to reporters at their Union City apartment and shared photos of their nephew until FBI agents arrived at their door Friday afternoon.

Michael Whitaker, a spokesman for the FBI's New Jersey office, confirmed agents were in the area.

"FBI Newark is in the vicinity in Union City conducting official law enforcement activity," Whitaker said.

Staff writers Ted Sherman, Jessica Remo, Vinessa Erminio and the Associated Press contributed to this report.

Kelly Heyboer may be reached at kheyboer@njadvancemedia.com. Follow her on Twitter @KellyHeyboer. Find her at KellyHeyboerReporter on Facebook.