The records 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.
The latest rampage occurred amid a debate over USA gun laws that was given fresh impetus by the massacre in February of 17 people at a high school in Parkland, Florida.
She said they were "afraid" to answer questions about their strong support for gun rights and the National Rifle Association.
Two Madden NFL players, Eli "True" Clayton and Taylor "SpotMePlzzz" Robertson, were killed in the incident.
Relatives of Clayton read a statement to reporters in Jacksonville.
Clayton's cousin, Brandi Pettijohn, spoke on the family's behalf, saying family was "devastated by yet another senseless act of gun violence".
"I think personally I'm one of the better players", he said.
Jacksonville Sheriff Mike Williams said authorities believe Katz carried out the attack using at least one handgun at the Jacksonville Landing, a collection of restaurants and shops along the St. Johns River.
Police named the shooter as 24-year-old David Katz from Baltimore, Maryland, and said he was in Jacksonville for the competition.
EA, the gaming company behind the Madden series games, announced on Monday that it would cancel the three remaining Madden Classic qualifier events following the shooting, including tournaments GEXCon, due to take place at the Dulles Expo Center in Fairfax County from Friday to Sunday.
Nine other people suffered gunshot wounds and two people were injured fleeing the area, the Jacksonville Sheriff's Office said. Police have not released a motive. He was prescribed antipsychotic and antidepressant medications, as well. He also said Katz was eliminated about 15 minutes before the shooting began.
There was no security during the tournament and the room it was held in was small, Casey said.
Police said surveillance footage from inside the restaurant hosting the competition showed a lone attacker walking by other patrons and going to the backroom, where the contestants had assembled and were playing.
The FBI said in a recent study of dozens of active shootings that attackers, frequently fueled by grievances in their lives, obtain their guns legally and then target specific victims.
Devin Jett of Washington, D.C., who has been playing Madden since 2006 and participates in organized events, said most of the people who compete have played together; some even work on strategy together, a practice called "labbing".
"He was kinda upset about that, so I'm guessing that had something else to do with it, too", Madunic said.
A gaming rival of the former gaming champion suspected of killing two competitors, wounding nine others and killing himself recalled him as "being kind of different".
Kivlen was at his Jacksonville hotel when the shooting happened Sunday.
The players blissfully forgot about the problems of the real world, deeply engrossed in the virtual world of competitive gaming. Reports say that Katz was an introvert and mostly "meant business". Katz's two known hospitalizations as an adolescent did not reach that threshold. But after winning a championship previous year, Kivlen says Katz "got up and let out the weirdest scream ever".
The tournament was live streamed on Twitch when suddenly gun shots were heard after which the game was abruptly stopped.
Jacksonville Sheriff's officers patrol around the ships at Jacksonville Landing on August 26, 2018, in Jacksonville, Florida. He died of a self-inflicted gunshot wound.