Harry Angel uses a set of expensive skeleton keys to open locked doors. *It is also a reference to a "Hand of Glory" which Margret Krusmark mentions as well.
The song Girl Of My Dreams, which Louis Cyphre (Robert De Niro) plays at the end, is the same song that Epiphany Proudfoot (Lisa Bonet) sings in the bathtub earlier (and identifies as a Johnny Favorite tune that her mother always sang to her).
It also has several appearances in the soundtrack: in Courtney Pine’s saxophone solos, and played in a ghostly, one-fingered style on an out of tune piano.
As for Rourke, today Angel Heart looks like his pinnacle as a proper movie star, a film home to a classic antihero turn delivered before the actor’s overpowering self-destructive tendencies would cast him into the wilderness for much of the 90s and 00s. He would never be cooler, never more doggedly charming and, by the end of the film, never more hauntingly anguished.