I believe that when he was admitted to the Workhouse (and appears to have taken on the mantel of David COHEN), he was a raving lunatic in the truest sense of the word? He certainly didn't just wake up one morning as such. If we are to believe that he was (that mad), then how on earth can we expect him, to have solicited his victims and indeed have earned their trust, taken them down a dark alley and dispatching them. Is it not more credible that if COHEN was in fact as mad as they say he was, then people would have given him a wide birth? I would also argue that local people would have known him (if not by name) then certainly by some nick name and had he been seen with any of the victims this would have been identified as such.
Granted the populace of the area was vast, but people of this ilk tend to stand out and be noticed, I suppose I could use the example of leather apron for this, people knew him if not by name (not that leather apron was mad or anything, but you understand what I mean). I would hazard that every community has an individual of this type or another?