JACKSONVILLE, Fla. – The 24-year-old man accused of opening fire Sunday afternoon at a "Madden NFL 19" regional tournament at the Jacksonville Landing, killing two and shooting 10 others, clearly targeted fellow gamers, Sheriff Jacksonville Sheriff Mike Williams announced Monday.

Williams said 24-year-old David Katz, of Baltimore, had two handguns with him -- a .45-caliber and a 9 mm -- and extra ammunition when he entered Chicago Pizza and headed to the Good Luck Have Fun Game Bar.

Williams said there were about 130-150 people in the restaurant and bar at the time.

"He walked past patrons in other parts of the business and targeted gamers," Williams said. 

Surveillance video clearly shows a gunman, and it appeared that Katz only fired one of his guns.

A  livestream of the tournament captured gunfire, shouts and screams about 1:30 p.m. The crowd scattered, some taking refuge at Hooters restaurant and other open businesses at the Landing.

Others of what rescuers called the walking wounded found firefighters involved in a training exercise nearby before the first 911 calls were made.

The Landing went on lockdown while a SWAT team and the bomb squad went through the building, finding survivors hiding and make sure there were no other threats.

Martin Lopez, a former military security intelligence specialist, says the gaming room where the shooting occurred is an example of a soft target.

“This is the kind of place criminals look for," Lopez said. "It’s a relaxed environment and people aren’t paying attention or keeping an eye out for what’s happening around them.”

WATCH: Security expert explains how game room was soft target

One day after the gunfire, Williams said investigators still have not identified his motive for the shooting. He said both guns, one equipped with an after-market laser sight, were recently purchased legally in Maryland.

The shooting took place at the first of four regional qualifiers, offering a $5,000 prize to the winner. The top six placing at the tournament would advance to the national championship in Las Vegas in October. Top prize there is $25,000.

About the gunman

Monday afternoon, News4Jax learned from court records that Katz had been for mental illness.

Divorce filings from Katz's parents show that, as a teenager, he was twice hospitalized in psychiatric facilities and that he was prescribed anti-psychotic and antidepressant medications.

The records also show Katz's parents disagreed on how to care for their troubled son, with his father claiming his estranged wife was exaggerating symptoms of mental illness as part of their long-running and acrimonious custody battle. The couple divorced in 2007.

Katz, a former Madden NFL champion, was recalled by a gaming rival as "being kind of different."

Shane Kivlen, 21, of Seattle, was the best friend of one of the gamers who was killed in Sunday's shooting at the southeast regional finals for the Madden 19 Championship being held a game bar inside Chicago Pizza.

"It just doesn't make sense why he would do it," Kivlen said. "In 'Madden,' you never get so mad at a loss that you would want to do that."    

Kivlen said Katz didn't talk much with fellow gamers, either online or when they met face-to-face for tournaments. He said much of what he and others knew of Katz they learned from his baffling style of playing the game.

Kivlen says Katz was smart, "but something was off about him."

He says Katz wasn't known to trash talk with rivals. But after winning a championship last year, Kivlen says that Katz "got up and let out the weirdest scream ever."

Kivlen was at his Jacksonville hotel when the shooting happened Sunday.