Well no not necessarily.. There are other things like them shooting a gun, but they can also have residue on their hands and just been shot.Not "no guns at all anywhere" but no guns next to bodies. If they had fired in self defense then been killed, their weapon would be next to their body. No weapons were found next to any bodies or this would have immediately been a suspected murder suicide.
Gary obviously didn't commit suicide but he could have gotten a shot off.
They haven't said yet, but I'm not sure yet it is a given that one or two of the victims didn't get a shot off at all.