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.
I know the pattern of drug abusers, especially the ones that are addicted to hard drugs. They get arrested for possesion... They get realeased and get probation... They don't get a job, but they find a way to manipulate and steal and feed their drug addiction once more... Another arrest ensues... This time maybe a drug rehab is in order? The released once again... This cycle of arrests and releases repeates over and over till you find a serious crime occurs as in death and or rape. I know this is a generalization, but an accurate ine.