I disagree as drug abuse in the fashion of most abusers leads to deviant/criminal behavior. Given a slap on the wrist like this case made an opportunity for this piece of excrement to strike down an innocent girl.
I don't think drug abuse per se has anything to do with the kind of deviant behavior we're seeing here, if you discount the rare occasions when extreme usage might lead to psychosis. I can see where the association might be made, but I don't think it's a good one. This individual is most likely a sociopathic "recreational" killer, who would do what he does regardless of whatever influence drugs might have had on his behavior in the past. You might argue that going out of the way to prosecute such a person for drug use would prevent such a thing from happening, but that would be true only if the penalty for drug use were life imprisonment.