Honestly, I don't want to talk guns vs. no-guns. This man could have had a Samurai sword and walked up and decapitated / stabbed these people, as oblivious as they seemed to be.
He was nuts. He was also probably paranoid (everyone out to get him, keep him down, etc). This is a common trait of high-control groups and Cults - PARANOIA and the "Us vs. Them" mentality that they shove down your throats from the cradle to the grave. He may have thought these people had demons in them and were trying to hold him back in life......persecuted by white demons, etc and in his disgruntled mental state, up and killed them.
And like one poster stated above, all of these cases of murder by JW's is really high. Is it any wonder? Cult members (and ex-members) tend to be depressed, anxious, paranoid, schizos, angry, suffering from PTSD, etc, etc.