Let's not have this be another debate about gun control while ignoring the real issue here that this was a terrorist attack. American gun laws are crazy and gun control is needed, however let's not kid ourselves here. Gun control will not stop terrorist attacks of this kind. It didn't stop them in France and it didn't stop them in Beligium and it wouldn't stop them in the US. This could happen anywhere.
On this occasion the real issue is security. You should not be allowed to just walk into a nightclub with a gun unnoticed. Guns don't belong in these places because guns and alcohol don't go well together and I'd bet this nightclub does have a no gun policy. Guns don't belong in any kind of gathering like this so why not stop them being brought in? Metal detectors should be compulsary at the entrance to venues that host crowds and bags should be searched. I've been to nightclubs in London where this happens and it's the only place I've seen it. It needs to be compulsary everywhere. That's the reality of the world we live in today.