A co-worker of the suspect in the Orlando, Fla., nightclub shooting described Omar Mateen as homophobic, "unhinged and unstable," according to Florida Today, a daily newspaper in Melbourne, Fla.

ADVERTISEMENT

Daniel Gilroy worked with Mateen at G4S Security for several months in 2014 and 2015 and said Mateen frequently made homophobic and racial comments.

He also said Mateen began sending him multiple texts a day, leading Gilroy to quit his job.

"I quit because everything he said was toxic," Gilroy said. "And the company wouldn't do anything. This guy was unhinged and unstable. He talked of killing people."

Fifty people, including Mateen, were killed and 53 more wounded inside Pulse, a gay nightclub. Mateen, a U.S. citizen from Florida, is suspected in the shooting.

Orlando Police Chief John Mina told reporters the suspect had an assault-style rifle and a handgun. The Islamic State in Iraq and Syria claimed responsibility Sunday for the shooting but offered no proof for the attacks.

The FBI confirmed on Sunday it had interviewed Mateen three times before the shooting took place early Sunday morning.

An official said the FBI first became aware of the suspect in 2013 when he made "inflammatory comments to coworkers alleging possible terrorist ties."

In the course of that investigation, Mateen was interviewed twice, but the FBI was unable to verify the substance of his comments.

Again in 2014, the FBI conducted an investigation into possible ties between Mateen and an American suicide bomber.

The FBI conducted another investigation, which included an interview with Mateen, but determined that the contact did not constitute a threat at that time.