The murder-suicide occurred during a Madden NFL 19 video game tournament in a restaurant at the Jacksonville Landing, a waterfront retail and entertainment complex in downtown Jacksonville. Another followed two minutes later.
Police have yet to officially identify all the victims, but several survivors spoke up on social media following the shooting.
The tournament was taking place at the GLHF Game Bar of a Chicago Pizza.
"I've been telling them this, like, I've been telling them this for a while that we need, you know, you need to make players feel safe", Jones said.
Divorce filings from his parents say that as a teenager he was twice hospitalized in psychiatric facilities and that he was prescribed anti-psychotic and anti-depressant medications.
"I'm still shocked, I can hardly talk", he said.
They started treating people and found the three victims, including Katz's body. Madden 19 is the latest NFL football video game put out by sports game publisher EA Sports.
Police located and searched Katz's Jacksonville hotel room and federal agents searched his home in Maryland.
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He had nearly 900,000 subscribers on YouTube and hundreds of thousands of followers on Twitter. Heitmann showed the vehicle to his audience in a December 2017 YouTube video embedded below.
He was known to barely speak to fellow gamers and sometimes exhibited an erratic playing style, according to other competitors, who were baffled that their virtual sport could lead to bloodshed.
Florida Governor Rick Scott met with local and state law enforcement officers and tweeted a thanks to Jacksonville Fire and Rescue, whom he credited with rushing toward the shooting in order to save lives.
A Twitter message from the winning team in 2017 identified Katz as the victor of the Madden tournament, held that year in Buffalo.
Johnson barricaded himself and some customers in the restaurant and grabbed two knives, adding, "If you come into this kitchen, you're bound to get stabbed".
"He was weird all weekend, I mean he had shades on, he just - he didn't speak to anybody", the man said. Our hearts go out to all those affected. Alston said he took cover during the ordeal.
EA Sports, the video game company behind the Madden franchise issued a statement on the shooting, calling it "a senseless act of violence that we strongly condemn".
"To have someone walk into an event like this that's all about good sportsmanship and teamwork and just good vibes, and do something like this, it's heartbreaking", he said.
Gjoka tweeted: "I will never take anything for granted ever again".