David Katzkilled two and wounded 11 in a shooting at a Florida gaming tournament.
Police say the motive is still unclear, and it is unknown if the victims were known to the suspect.
"The hardest part for me is he was a young guy", Garret Scartace, one of Clayton's former high school teammates, told the Times. His principal, Catherine Foss, remembered him as "a leader" in a news briefing Monday morning at the campus. "His mother was an awesome woman who was incredibly close to her son". "He loved his family more than anything".
"He stuck up for other people, he was kind-hearted, and he was a joy to be on our campus", she added.
Early media reports suggest that Katz was upset to have been knocked out of the tournament. I went to shake his hand and just tell him good game and he just looked at me. The "Madden" game's maker, EA Sports, lists a David Katz as a 2017 championship victor. Lopez said the shooting at the Jacksonville landing played out in a room about the size of a large bedroom.
Mr Roberston who took the handle "SpotMePlzzz" was also a successful player, having won the Madden 17 Classic. "This is your chance to earn your spot in the first Major's Live Finals happening in October 2018", the Facebook page for the event reads.
Madden is the official video game of the National Football League. He said when the shooting started, he immediately dropped to the floor.
Electronic Arts, developer of the Madden series of football games, sent out an extended message regarding Sunday's tragedy both on Twitter and, according to players' tweets, from inside of the Madden 19 game.
The couple said people trampled others in the panic to escape.
The video does not show the shooter, but many gunshots could clearly be heard, while a red laser sight - presumed to be from the handgun - was visible on the shirt of one of the victims before the video cut away. One witness described the "pop pop pop" sounds that "didn't stop".
"The suspect clearly targeted other gamers", said Jacksonville Sheriff Mike Williams. Dave Fitz told The Associated Press that agents went to the upscale townhouse home of the man's father in Baltimore, but didn't release any further information, citing the ongoing investigation.