David Katz, inset, shot fellow gamer Eli 'Trueboy' Clayton, right, who is shown with a laser pointed at his shoulder.

WARNING: DISTRESSING CONTENT

A livestream of an NFL gaming tournament has caught the chilling moment a laser landed on the chest of a player before a rival shot him dead.

David Katz, 24, killed himself and two others, and left 11 people injured in the chaotic shooting at the Jacksonville Landing complex in Jacksonville at around 1.34pm on Sunday (US time), police said.

According to friends and family, the two men that Katz killed in the tournament were Taylor 'SpotMePlzzz' Robertson, 27, of Ballard, West Virginia and Eli 'Trueboy' Clayton, 22, of Woodland Hills, California.

Robertson was married and father to a young son, and had won 72 per cent of his 18 prior matches in Madden NFL tournaments, according to EA Sports. Clayton was a rising star in the Madden community.

Police have not yet confirmed the identities of the deceased victims. Local media, including the Miami Herald and ActionNewsJax, have named Robertson and Clayton as the deceased victims.

An official close to the investigation said that the gunman killed himself with the semi-auto handgun used in the shooting, which had a laser sight.

Nine other people were wounded by gunfire and all were in stable condition on Sunday evening after being taken to hospitals. He added that two others were injured in the rush to flee the gunfire.

Katz was in Jacksonville for the "Madden NFL 19" video game tournament, authorities said. The games maker, EA Sports, lists a David Katz as a 2017 championship winner.

The competition was held in a gaming bar that shares space with a pizzeria. Viewers could watch the games online and see the players.

Investigators were looking into an online video that appeared to capture the scene right before the shooting began, Williams said. A red dot that appears to be a laser pointer is visible on the chest of a player seconds before the first of about a dozen gunshots rings out.

'He is not here to make friends'

About 150 gamers competed in the competition for a US$5000 prize. The winner was set to go on to a finals tournament in Las Vegas with a US$125,000 prize.

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One of the gamers to defeat Katz in the tournament told ActionNewsJax that Katz was acting "weird" on Sunday and wearing the same clothes he wore yesterday, the first day of the tournament.

The gamer said that when he beat Katz on Saturday in the pool round, he tried to shake his hand, but that Katz just stared blankly.

An announcer for one of the gaming tournaments Katz previously played in described him thus: "He is not here to make friends. He's all business, he's focused, and to even get him to open up to talk to you about anything - it's like pulling teeth, man."

One witness to the shooting on Sunday, Javarius Long, told the Tampa Bay Times that the shooter was "nerdy".

Long said that Katz got mad after losing in the elimination round, left the venue presumably to retrieve the gun from his car, and came back and started "blasting everybody".

Marquis Williams, 28, and his girlfriend, Taylor Poindexter, 26, both from Chicago, were ordering pizza at the bar when they heard the first shot around 1.30pm on what had begun as a quiet Sunday afternoon.

"Initially we thought it was a balloon popping, but there weren't any balloons in the room," said Williams, who had taken part in the tournament earlier. "Then we heard repeat shots and we took off running."

He added: "The first shot everybody just turned and looked. After the second, third and fourth shots, everybody took off and ran for the exits."

Poindexter, an aspiring gamer, said she had gone to seek experience at the tournament. She never saw the face of the shooter, but added, "We did see him with two hands on a gun walking back just popping rounds."

It was then, they said, that people trampled others in the panic to escape. Both ran to a nearby restaurant where workers were waving people inside. They hid in a bathroom until police arrived.

Jason Lake, the founder and CEO of compLexity, a company that owns professional esports teams, said on Twitter that one of his players, 19-year-old Drini Gjoka, was shot in the thumb.

Gjoka tweeted: "The tourney just got shot up. Im leavinng and never coming back." Then: "I am literally so lucky. The bullet hit my thumb. Worst day of my life."

On Sunday evening, the FBI said, its agents searched a family home of the man authorities believed was behind the attack.

Heavily armed agents, some in bulletproof vests and brandishing long guns, could be seen entering an upscale townhome complex near Baltimore's Inner Harbor.

An FBI spokesman, Dave Fitz, confirmed that agents had gone to the house of the man's father in Baltimore. He declined to release specifics, citing the ongoing investigation. TJ Smith, chief spokesman for the Baltimore Police Department, also said that agency was assisting law enforcement partners "with some information that has led authorities to Baltimore."

In Washington, White House spokeswoman Sarah Huckabee Sanders said President Donald Trump had been briefed on the attack and the White House was monitoring the situation.

The governor of Florida with my son @oLARRY2K pic.twitter.com/nP0VCLUyYY

The Jacksonville Landing, in the heart of the city's downtown, also hosts concerts and other entertainment. It was the site of a Trump rally in 2015, early in his campaign for the White House.

The sheriff's office used Twitter and Facebook immediately after the shooting to warn people to stay far away and to ask anyone who was hiding to call 911. Police also barricaded a three-block radius around the mall and sent in a SWAT team and bomb squad experts to secure the area. Police also took up positions on a bridge spanning the river with a view of the area.

- AP, Daily Mail

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