At least three people (including the shooter) have been killed and several others have been injured. You can here disturbing audio of the shooting here.
The Jacksonville Sheriff's Office reported two hours ago that one suspect was dead at the scene of the shooting. They were not sure if there was a second suspect.
My son does gaming tournaments, so this is all a bit more jarring to me than other recent mass shootings. Which is an admittedly sad admission on my part...
Updated later on 08/26/18: It's been announced that their shooter in today's mass shooting is 24-year-old David Katz. Katz won a previous Madden gaming tournament and was registered to play in this weekend's event. He reportedly took his own life.
It's not clear why he began shooting the others at today's event.