"The gamer added: "[He was here] all weekend. The police are still looking for a motive and whether Katz knew the victims.
It's believed Katz was disgruntled for losing the match, returning to the Game Bar attached to Chicago Pizza in Jacksonville Landing while a game was streaming live - to carry out his attack.
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.
Katz was an avid gamer and has participated in various Madden tournaments in recent years.
The gunman, Katz, was a professional gamer himself.
A tweet by National Football League team Buffalo Bills two years ago shows a picture of a man named David Katz holding up a t-shirt that says "Madden champ", with the caption: "Congrats to David Katz, the Madden 17 Bills Championship victor!"
A gaming rival of the man blamed for a deadly shooting rampage at a video game tournament says he's baffled that anyone he had competed against online would resort to bloodshed.
"I've been telling them for awhile, that they need to make this place safe", Jones said. Williams said people trampled each other trying to get away.
In a post-game interview following his win, Katzs face could be described as emotionless, while his eyes wander from looking at the floor to around the room.
Two people were fatally shot and another 11 were injured after a 24-year-old man opened fire on a high-stakes esports tournament at a Florida mall Sunday. The tournament was the Southeastern Qualifier for the Madden NFL Championship Series. One person was taken to Baptist Medical Center with a minor injury. He adds, "We are committed to supporting Taylor and Elijah's families through this hard time, and we send our deepest sympathies to their loved ones, to those injured yesterday, and everyone affected".
He had earned about $51,000 playing Madden football and Robertson had earned about $80,000, EA Sports said on its website. "We are working with authorities to gather facts at this stage".