Around 150 gamers competed in the competition for a $5,000 prize.
The records show Katz's parents disagreed deeply on how to care for their troubled son.
Katz, who was 24, was prescribed a number of psychiatric medications, including an antipsychotic, and saw "a succession of psychiatrists", according to a 2006 letter from the father's attorney. Ten other people were injured by bullets and the shooter, identified as David Katz, shot and killed himself.
"There are prior relationships with - I don't know specifically about which victims, but this group travels kind of as a circuit, so they are familiar with each other".
The Jacksonville Sheriff's Office initially said on its official Twitter account that police were responding to a mass shooting at The Jacksonville Landing, a riverfront strip of restaurants, bars and shops that runs along the St. Johns River. Katz attended Hammond High School in Columbia, Maryland, and went on to the University of Maryland beginning in 2014.
EA Sports CEO Andrew Wilson cited "a comprehensive review of safety protocols for competitors and spectators" in a statement announcing the cancellations Monday evening. All of the injured are expected to survive, he said.
"As you can imagine, we are devastated by yet another senseless act of gun violence", Clayton's cousin, Brandi Pettijohn, said while reading a statement. Clayton was a rising star in the gaming community at Madden.
"@SirusTheVirusTV and @fitzmagic13 dad are heroes", said pro "Madden" player Jokeeee. "He made a good living gaming, and he saved his earnings so he could afford to go to college to continue his education".
UK PM May for Abuja, Lagos tomorrow
Mrs May's visit to Nairobi will mark the first by a United Kingdom prime minister to Kenya since Margaret Thatcher in 1988. May says she raised the issue with Ramaphosa when he was in London earlier this year.
"They are always here, that's what I can tell you".
Fellow gamers described Robertson as a family man dedicated to his wife and children.
"My first reaction, I heard the shots and I thought, 'Why is there firecrackers in here?' " Montagnino said Monday. "He's got a family at home, and he just came out here to try to win some money for this family".
"I want to extend our prayers and condolences to the victims of the tragic shooting in Jacksonville, Florida", the President said.
"We've always known he was a little off and stuff just because he wasn't social at all", Kivlen said, adding that Katz's odd behavior extended to his game play. We're expecting more information on them today.
Court documents also quoted his father, Richard Katz, as saying that the pair would call the police on each other about very trivial matters, such as David complaining that his mother was watching too much television and her alleging that he spent too much time playing video games.
Experts in Maryland say the video gaming gunman's history of mental illness apparently wouldn't have stopped him from buying guns before he killed two people and wounded 10 and then killed himself at a tournament in Florida.