/ Updated 
By Julie Compton

As investigators look into what may have motivated Omar Mateen to go on a shooting rampage at Pulse nightclub in Orlando early Sunday morning, reports are surfacing that it was not his first time at the popular gay venue.

"Sometimes he would go over in the corner and sit and drink by himself, and other times he would get so drunk he was loud and belligerent," Ty Smith, a frequent patron of the nightclub, told the Orlando Sentinel.

An FBI official, speaking to NBC News, said other members of Orlando's gay community remembered seeing Mateen at Pulse prior to the shooting, and a man told MSNBC he received messages from Mateen on Grindr, a popular dating app for gay and bisexual men.

The allegations about Mateen's multiple appearances at Pulse and his usage of gay dating apps have fueled speculation about his sexuality in news reports and on social media.

GLAAD, an LGBTQ advocacy group that focuses on media, also released a statement addressing the speculation.

“This atrocity was an attack on the LGBT community, it was an attack on our country, and it was an attack on the core American values of equality and freedom for everyone. Whether the gunman’s homophobia spurred from hatred of others or hatred of himself, this is homophobia all the same. And it’s sadly just the latest example of homophobia turning to horrific violence, just as it has for decades," wrote GLAAD President & CEO Sarah Kate Ellis.

“Being homophobic might be your way of proving to yourself that you’re not homosexual - after all, you are homophobic. [It] can be a powerful driving force for hate."

If "hatred of himself," as Ellis phrased it, in some way contributed to Mateen's horrific actions, he could have been experiencing what psychiatrists call "reaction formation." According to psychiatrist Daniel Linhares, this is an "ego defense mechanism" that happens at a non-conscious level where a person experiencing unwanted feelings goes to great lengths to prove those feelings are not real.

“Being homophobic might be your way of proving to yourself that you’re not homosexual - after all, you are homophobic. [It] can be a powerful driving force for hate,” said Dr. Linhares.

"It could have been that someone in this mindset would even frequent gay nightclubs under the conscious pretext of planning an attack, while unconsciously they are actually satisfying a hidden desire," he added.

Examples of reaction formation are all around, Linhares said, but they are typically not deadly. Just think of recent examples of anti-LGBTQ politicians and religious leaders who been exposed as gay or bisexual. Linhares said extreme cases of reaction formation, however, can end in violence if the person experiencing them is emotionally immature, mentally ill or suffers from an addiction.

While Linhares, who has never met Mateen, said he can't speculate on his motives for the attack - since that would require a thorough psychiatric evaluation - nor his sexuality, he did stress Mateen was not simply a victim of society, "because people make their own choices.”

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Brooke Sopelsa contributed.