The thing is that most books are written by people who have made up their mind about it and show evidence for theit view on the case. However it's hard to say who it was al the sugestions from you guys are pretty good. But why would Tumblety stop killing when he got to America. I think Druitt might be a good guess as he comitted suicide which explains why nomore people died. Sickert seems unlikely.
If I should pick one I think I'd say Druitt, but I'm not sure, it could be anyone, even someone who nobody has even thought of. Random bum with some knowledge about anatomy etc.
Tumblety went "off the map" when he returned to the USA until his death Scotland Yard even send agents over to America to try and track him down so i think to do that back then must have shown they had a good knowledge of who he was
when he died the nuns at the hospital found two imitation gold rings on his possession identical to the ones taken from one of the victims
he collected wombs
in London an American Dr had been asking around the hospitals and medical schools for wombs at the time
he is believed to be the "Batty street lodger " who was according to the landlady a american doctor who came back to the lodgings the night of the doubble event with blood on his cloths also batty street is about 100 yards from the first murder sight
at the time a posh london hotel had a american dr staying there who was apparently in the habit of "slumming" in the East end when he vacated his room they found a bag containing "obscene publications" aka victorian advlt material as a boy Tumblety sold similar material to the canol workers in Rochester New York
to me all these ponts just click into place placing him as the murders but that is just my opinion =]
oh and his wife was secretly a prosttute he found out by following her and seeing her going tinto a brothal with other men this explains why he would vent his anger at these particular types of women