Local authorities identified the gunman as 24-year-old David Katz. He had been participating in a tournament for the Madden football game franchise, and was among those pronounced dead at the scene.
Jacksonville Sheriff Mike Williams identified the suspect at a news conference Sunday evening, saying the FBI was assisting with the investigation.
Three people were killed, including the gunman, Williams said. Nine others were shot, and two were injured while fleeing.
“This number may change as we learn of people who transported themselves” to hospitals, Williams said.
The first 911 calls came around 1:34 p.m., with reports of a shooting at the Chicago Pizza at the Jacksonville Landing, a collection of shops and restaurants along the St. Johns River, where a Madden 19 video game tournament was being held. SWAT and bomb teams swept the area and surrounding stores were on lockdown, Williams said.
Baltimore Police spokesman T.J. Smith said in an email that “we are assisting our partner law enforcement agencies with some information that has led authorities to Baltimore.”
Federal authorities were at a home in the 1200 block of Harbor Island Walk near Baltimore’s Inner Harbor on Sunday night as part of an investigation into the Jacksonville mass shooting.
Matt Munoz and Cameron Stearns were eating dinner next door when they saw agents with rifles walking around the back. "It's like, 'Uh, what's going on?' " Munoz said.
They were briefly interviewed by agents, who asked among other things if ammunition had ever been mistakenly delivered to their home.
A gunman opened fire at an online video game tournament that was being livestreamed from a Florida mall, killing two people and then fatally shooting himself.
By Antonia Noori Farzan, Alex Horton and Kristine Phillips and Peter Hermann
Aug 27, 2018 at 9:02 AM
Stearns, 33, said he had seen Katz but never spoken to him beyond cordial greetings. "I definitely had seen him coming and going from the house. The FBI guy showed me his picture, and I was like, that’s definitely him," Stearns said. "When he was younger he definitely lived here. Now, I’m not so sure. I hadn't seen him as frequently."
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The police activity in the neighborhood was "shocking, to say the least," Stearns said, adding that the area is very quiet and rarely sees even petty crimes.
Earlier Sunday, people in the online gaming community had identified Katz as the shooter, and said he had played under the game tag “RavensChamp” and “Bread.”
Video game tournaments have been growing in recent years, with winners competing for thousands of dollars and other prizes. One of the tournaments Katz won last year had play-by-play commentators, and he was interviewed by former NFL player and broadcaster Steve Tasker, according to a YouTube video.
“Personally I think I’m one of the better players and I like to let my game prove that,” Katz told Tasker after defeating a higher seed.