arma virumque cano (et alia)
This kind of shooting seems to happen pretty often in this particular music genre. The only other genre that seems to mention guns a lot is the country/western genre, and you certainly don't see them shooting their professional rivals. The shooting seems to be a continuation of a series of that happening in the club which led to its closing. While I don't believe that the club's being a gun free zone facilitated the shooting, it certainly didn't prevent it.