Let's say, for arguments sake, that KJ was killed by a blow to his neck, then what happened? After walking into the gym, unseen by gym surveillance cameras, the killer has approximately 8 minutes (giving a minimum of two minutes for greeting/words, and then the karate chop), to dispose of KJ's body. He would have to carry dead weight onto 6' high mats, remove KJ's shoes, throw both the shoes he was wearing, strategically placed (black and white at his head), and then stuff his body into the rolled mat throwing the Griffins in after KJ. The shoes being placed inside to make it look like KJ was going after his shoes and thus, making the murder appear to be an accident.
The other scenario would be to pull down 20 or so mats, take down the blue mat, unroll it on the gym floor, wrap KJ's body into the mat, putting the black and white shoes at his head, removing the Griffins and placing them at his feet. The perp would then right the mat vertically, prop it against the wall and then stack the other 20 or so mats back into their vertical positions. The perp would then walk out of the gym unseen by the gym cameras. All in approximately 8 minutes.
Does that sound feasible?