People go crazy on drugs, but they only do so spontaneously if it is a crime of passion, for example, boyfriend or husband kills ex-girlfriend or cheating wife in the heat of the moment or plans it out very simply.
What I'm saying is that nobody just goes insane over night for no reason and kills a bunch of random strangers for no reason. Nobody is so insane that they don't have a motive for their murder. Sometimes it's political, sometimes it's relationship-oriented, but people don't just go nuts without some outside factors, whether those be drugs, money, relationhsip problems, whatever. The people denying any sort of foul play here would have us believe that this guy just randomly decided to kill a bunch of people and spent months and thousands of dollars planning it out, all while being influenced by nothing but his own craziness. People just don't do that.