Mr. Meticulous

If an articulate, albeit murderously psychopathic teacher tickles your inherent, non-so-funny-bone (keeping in mind that curiosity killed the cat), then by all means scratch it.

 He's an educated man is Mister Meticulous, a decent-to-good special needs teacher working in an inner-city slum - who suddenly morphs into a killer by dint of his own gross shortcomings, abysmal depravities and a sick society at large - a veritable "Perfect Storm" to facilitate these atrocities - like killing a trusted student for example, or the flawed, bovine dogma of your average ISIS recruit.

 And with the inherent empathy of a plastic flower (or your local neighborhood closet-psychopath, for that matter), Mr. Meticulous discovers the hardest way - that being too darned meticulously-inclined can get you killed real quick. It's Karma. And with the suitable flourish from a random murderer's heavily-calloused right hand - meet the once-respected special-needs teacher Mister Meticulous,  strap yourself down - and be good, for goodness sake.