Authorities have named Taylor "SpotmePlzzz" Robertson, 28, and Elijah "Trueboy" Clayton, 22, as the two people killed by a gunman at a "Madden NFL 19" qualifying tournament in Jacksonville, Florida, on Sunday.

The Jacksonville Sheriff's Office released the names of the two men Monday.

Clayton was engaged in a game in the tournament when shots were fired and caught on a video that has gone viral. His family spoke to reporters Monday.

"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. "Every person who has stood in this position has said that they never thought this would happen to their family, and we are no different.

"... My cousin has to bury her first born, and it is just as terrible as that sounds. Our family has been forever changed. Nothing will replace the love that we have for Elijah. There is a hole that will never be filled."

The Tennessee Titans and Robertson's professional esports team, Dot City Gaming, both put out statements mourning Robertson, with the NFL team saying he was a "husband, father and passionate Titans fan who represented us honorably each time he competed."

Court records obtained by The Associated Press show that David Katz, the man accused of killing Robertson and Clayton and then himself, had been hospitalized for mental illness.

Divorce filings from the parents of the 24-year-old say that as a teenager he was twice hospitalized in psychiatric facilities and that he was prescribed antipsychotic and antidepressant medications.

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

Jacksonville Sheriff Mike Williams has declined to comment on why Katz opened fire inside a gaming bar connected to a pizzeria at The Jacksonville Landing, a collection of restaurants and shops along the St. Johns River. Williams said he used at least one handgun in the attack.

Originally from Ballard, West Virginia, Robertson was a competitive "Madden" player for a number of years. He was a husband and a father of a 2-year-old boy.

In 2017, Robertson won the "Madden NFL 17" Classic, and in 2018 he competed on behalf of the Titans in the "Madden NFL 18" Club Championship. Robertson was defeated in the AFC semifinals of the "Madden 18" Club Championship -- which ran in conjunction with Super Bowl LII in Minneapolis in February -- by Michael "D3liveranc3" Pinter, who represented the Steelers.

Clayton was a competitive Madden player from Woodland Hills, California. He placed in the top five in the "Madden NFL 17" Classic, Bowl and Challenge and won $5,000 with by placing 25th in 2017's "Madden" Championship. According to EA's website, he is the sixth-highest money earner in competitive Madden.

The Associated Press contributed to this report.