Agents from the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) have searched the Baltimore home of David Katz, the man believed to be the gunman who opened fire on crowds at a video game tournament in Florida, killing two people and injuring 11.

The 24-year-old took his own life at the Madden NFL 19 competition at Jacksonville Landing, a popular waterfront shopping and dining area in the heart of downtown Jacksonville.

At least 11 more victims were taken to local hospitals, nine with gunshot wounds and two who had been injured while fleeing the scene, polcie said.

As ATF agents emerged from the Baltimore property, one was carrying a small box, another a bag, which they loaded into an unmarked minivan.

Matt Munoz, 30, who works in information technology, and Cameron Stearns, 33, have lived next door to the Katz house for eight years. They said they saw David Katz when he was younger and in school but not so much as he got older.The last time they saw him was a month or two ago, they added.

“It’s not so much anymore,” Mr Stearns said as he and his roommate stood outside with neighbours and watched federal authorities. Mr Stearns said they were eating dinner when they looked out a window and saw an ATF agent cradling an assault style weapon.

Mr Stearns said an FBI agent asked them questions including – he thought jokingly – whether any ammunition meant for Katz had ever been mistakenly delivered to his house.

Both said they rarely spoke to Katz’s parents and almost never to David. “There’s nothing remarkable about them,” said Mr Stearns, a special education teacher. “There’s not anything suspicious about them at all. We have lived here for a long time and we never talk to them.”

Mr Munoz said an FBI agent showed him a picture of Katz. “I said, ‘Absolutely that’s him.’”

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At 10:30 pm, five police officials, including ATF agents, left the Katz home. They carried nothing. Nobody answered the door. An upstairs light turned off as reporters stood outside.

A neighbour, Jerry Knauer, said his wife last saw David Katz about two weeks ago. He described the father as “a really nice guy”. He added, “I feel sorry for him.” Speaking of the shooting, he said: “It truly is a tragedy”.

Mr Knauer was out when authorities started to search the house. They were escorted inside by ATF agents. Mr Knauer said he knew nothing about David Katz.

On Twitter, the FBI’s Baltimore field office confirmed that they had been assisting the Jacksonville sheriff’s office and ATF with the investigation in South Baltimore. At 10:45 pm, they announced that they had cleared the scene.

Esports tournaments such as the event involve professional competitors vying for prize money in games that are often streamed to thousands of online spectators. Prominent esports players carry endorsement deals and legions of fans, much like professional athletes do. Esports events and leagues are usually organised around a popular video game title. They include sports based titles, like Madden as well as real time strategy games, fighting games or first-person shooter simulations.

Competitors usually concentrate on one game or at least limit themselves to a certain genre. The tournaments vary in size and scope, some running several hours at informal locations, while others span multiple days and pack professional stadiums for championship events that can carry prize purses in the millions.

Others, like the Madden event in Jacksonville, are smaller tournaments leading up to larger events later in the calendar year. The Jacksonville event was a regional qualifier leading to an October final in Las Vegas, with a top prize of $25,000 (£19,000). It was unclear how many players were in the mall when the shooting occurred.

Players train regularly and rigorously for such events, with top professionals dedicating dozens of hours a week to practising their preferred game. Some esports leagues have formalised contracts that pay players an annual salary, sometimes in the five-figure range. The competitors and their fans often form tight knit communities, discussing the intricacies of the game and the latest developments of leagues via online video platforms like YouTube and Twitch, as well as social media. Esports analytics firm Newzoo estimates the audience will reach 380 million people in 2018.

Electronic Arts, the digital interactive entertainment company in charge of the tournament, said it was aware of the shooting and is cooperating with law enforcement.

“The tragic situation that occurred Sunday in Jacksonville was a senseless act of violence that we strongly condemn,” the company said. “Our most heartfelt sympathies go out to the families of the victims whose lives were taken today and those who were injured.

“All of us at Electronic Arts are devastated by this horrific event, and we also join the community in thanking the first responders who were quickly on the scene.”

Video believed to be from a live stream of the competition on the gaming platform Twitch circulated on social media after the shooting. It showed a red laser dot briefly appearing on a competitor’s sweatshirt before the camera angle switched back to the video game and more than a dozen gunshots rang out. The competitor has not been identified, and it’s unclear whether he was hit.

Danny Flaherty, a 22-year-old gamer from the United Kingdom, said that he heard gunshots and that his “only thoughts” afterward were “to run”.

Another player, Drini Gjoka, 18, said a bullet hit him in the thumb.

“I will never take anything for granted ever again,” he wrote on Twitter. “Life can be cut short in a second.”

Complexity Gaming, the company that sponsors Gjoka, said he ran down the street to a gym.

“We’re obviously shocked and saddened by this afternoon’s events ... He’s currently cooperating with the authorities and we will be flying him out of Jacksonville as soon as we are given the green light from the officials on the ground,” Complexity Gaming founder and chief executive Jason Lake said in a statement.

Gjoka, who is from the Washington, DC area and attended Woodrow Wilson High School, told the school’s paper earlier this year that he made $120,000 (£93,000) playing Madden.

Clay Taylor, an esports agent based in Ontario, Canada, heard about the shooting while on vacation with his family. He messaged one of his new clients over Twitter to see if he was OK. That’s when he saw the tweets saying “Rest in peace.” Then, he saw the video.

Taylor recognised his client, who was wearing a red sweatshirt and white headphones. Just before the shooting began, the live-stream captured a bright dot of light crawling up his chest. “Once I noticed the laser on his chest I knew what happened,” Taylor said in a Twitter DM. “I was so scared, angry and sad.”

As of Sunday night, police had not yet named any of the deceased or injured victims. On social media, however, members of the gaming community circulated the names of two gamers believed to have been killed in the shooting, including Taylor’s client.

Six male shooting victims in their early- to mid-20s were treated at the University of Florida College of Medicine in Jacksonville, four of whom were shot in the torso, said Marie Crandall, the attending trauma surgeon. The two others were shot in the extremities. One victim is in serious condition, but all are expected to survive.

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Three other shooting victims, now in stable condition, were treated at Memorial Hospital in southeast Jacksonville, hospital spokesman Peter Moberg said. A woman who was not shot, but was hurt while fleeing was treated for minor injuries at Baptist Medical Center, spokeswoman Cindy Hamilton said.

As of 9:35 p.m. on Sunday night, four patients had been discharged and were in good condition, the University of Florida College of Medicine said in a statement. Of the two remaining, one was in good condition, and the other was in serious condition and being monitored.

White House press secretary Sarah Huckabee Sanders said President Donald Trump was briefed on the shooting and was monitoring the situation.

The president did not address the shooting on Twitter on Sunday evening, instead writing, “Over 90% approval rating for your all time favourite (I hope) President within the Republican Party and 52% overall. This despite all of the made up stories by the Fake News Media trying endlessly to make me look as bad and evil as possible. Look at the real villains please!”

A poll released Friday by the Associated Press Norc Centre for Public Affairs Research put Trump’s approval rating at 38 per cent overall, and at 86 per cent among conservative Republicans.

Gun-control advocates seized on the moment Sunday to call for action against gun violence.

“My thoughts are with everyone impacted by the shooting today at the Jacksonville Landing – but thoughts are not enough,” House Minority Leader Nancy Pelosi said on Twitter. “As we continue to track developments, it’s clear Congress must stop stalling & act to protect Americans from the daily tragedy of gun violence.”

The Jacksonville rampage is the latest mass shooting to erupt in a public place – a wave of violence that has extended nationwide. Florida has experienced a number of high-profile mass shootings in recent years. The gunfire at the Madden NFL 19 competition came six months after a massacre at a high school in Parkland, Florida, that left 17 dead.

Parkland student David Hogg, who became a vocal gun-control advocate after the shooting there, tweeted to Florida's Republican senator Marco Rubio: “How many mass shootings in your state will it take for you to do something?”

National Rifle Association spokeswoman Dana Loesch, meanwhile, called for an end to gun-free zones and said security should be in place to keep people safe.

“A horrible tragedy. End gun free zones or have the security in place to keep people safe in them,” she tweeted.