Twitch, the platform that was live-streaming the tournament game during the shooting, said in a statement that, "we are shocked and saddened by the tragedy that took place in Jacksonville", adding that: "Twitch and all its staff send our deepest sympathies to the victims, their loved ones, and everyone in our community who's grieving".
As of the time of publication, police have not yet identified Robertson as one of the shooting victims. One suspect was dead at the scene, and it was unknown whether there was a second shooter, the sheriff's office said.
Florida has seen several mass shootings in recent years: a gunman killed 17 people at Marjory Stoneman Douglas high school in Parkland earlier this year; five people were gunned down at the Fort Lauderdale airport last year; and 49 were shot dead at the Pulse nightclub in Orlando in 2016.
Williams said Sunday evening that he couldn't comment on the suspect's possible motives. An FBI spokesman, Dave Fitz, said agents had gone to the house of the man's father in Baltimore. Police said they believed there were no accomplices. The event was at the GLHF Game Bar in Jacksonville.
The latest rampage occurred amid a debate over US gun laws that was given fresh impetus by the massacre in February of 17 people at a high school in Parkland, Fla.
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His grave site will overlook the Severn River, and will be next his best friend from his Naval Academy days, Admiral Chuck Larson. McCain's rebuttals were often more measured than Trump's brash rhetoric.
Florida Governor Rick Scott said he had offered state support in the aftermath, and that President Donald Trump had offered "any federal resources needed".
Video shared on social media showed players competing at a Madden football game before shots rang out. Within moments, a red laser dot appears on one of the players before the feed switches to the video game and gunshots are heard. Williams said investigators had seen the Twitch video. She said she saw Katz take aim at his victims. "I was scared for my life and my boyfriend's".
Others just straight up said she doesn't care about the shooting.
Another player, "DubDotDUBBY", said a bullet had grazed his head. "We're showing it live to whoever wants to come in and they can chit-chat and talk to me or just watch the gameplay". "Worst day of my life". "STAY AWAY #TheLandingMassShooting", the Jacksonville Sheriff's Office said on Twitter.
Nine other people wounded by the gunfire were all in stable condition Sunday evening after being taken to hospitals, Williams said.
National Rifle Association (NRA) spokeswoman Dana Loesch on Sunday called for an end or adjustment to gun-free zones in the wake of a shooting at a Jacksonville, Fla. entertainment center that bans firearms on the premises.