My interpretation was that Johnny himself killed all as a way to cover his tracks. He did this Subconsciously, with his Soul, as it were.
First up, I like the movie regardless of whether or not it's partly or wholly illogical, so this is moreso out of curiosity and convenience{the net} that I'm raising these questions.
I haven't finished re-watching yet, but there's plenty of things I'm curious about, for example does the timing have anything to do with anything, ie, the incident occurred in 1943, yet it's not till 1955 that Deniro becomes aware he was duped.
I think another good idea is to start at the start and work off the facts the movie presents us with, so am I right about this....
Favourite sells his soul to the devil, becomes rich/famous but suffers a severe head/facial injury, he's then rendered temporarily zombified{or was never zombified as that was a lie on Favourites part}, either way he has cosmetic surgery so he looks different and still has some form of memory loss.
He hatches a plan to use his accident as a means to escape his contract with the devil, so pays the doctor to falsify his condition/whereabouts, but for some unexplained reason, the lawyer and Deniro happened to be in the neighbourhood and discover the dupe.
I wonder whether we're supposed to know how it is Deniro finds out, or is that to be overlooked for the sake of the plot...?, either way, it's clear from the first meeting between Favourite and Deniro, that Deniro knows who Fav is, but Fav doesn't know Deniro and may not even know himself...!!
Given the name of the movie, Angel "Heart" and the Deniro egg scene, we can assume that Fav did consume or somehow use someone's else's heart in a ritual attempting who knows what exactly, but presumably some form of spiritual cleansing/identity swap, hence all the other players in the second part of the movie.
The trouble I'm having so far is that if Harry Angel knows the truth, then he'd never come back to deniro and inform him of what happened to the doctor, as it'd be obvious that Angel killed the doc and why, so we have to assume that either Angel didn't do it, did do it but his memory is in the way, or Deniro did it, so if Deniro is doing it, is it because he
doesn't know who the players are in the rituals/voodoo, and needs Angel to track them and identify them..?
That said, doesn't the ending show Angel doing it and then having an intense moment trying to reconcile who he really is...?