According to Wikipedia and The Brisbane Times, the term "Ismail Ax", which was found on the shooter's arm, is a reference to a nickname he used on some gaming sites and was his Xbox gaming tag. He also apparently used the name to sign his final letter with, suggesting he wanted it to be known that he was the same person, perhaps.
However, it is a little odd. Not least where he got the name from, and that he felt compelled to use it. The media jumping on the Islamic connection was obvious and to be expected because, well, the media could find an Islamic connection in a KKK rally if they felt inventive enough, and this was a bit more obvious than their usual scaremongering.
So yeah, apparently, we have a mentally ill gamer who had problems distinguishing between reality and fiction. Or at least, that is the picture being portrayed. So we can expect endless rounds of "ban this sick filth"-ists calling for every game that isn't Super Mario Kart to be pulled from the shelves, the gun lobby and NRA insisting the mentally ill be allowed any sort of weapon they want and inbetween, the victims basically not given a shit about except as political tools for various agendas.
Welcome to the 21st century.