|Steve said Diti thought Leonard was a skank, too. He certainly wore those gangster clothes well. I see him as a victim who takes control--he "sets Teddy up" as his wife's murderer, copying down his license plate number, because he knows Teddy's evil and the only way he can escape him is to trick his "core self" into believing that Teddy's the murderer. Then he'll have the strength and motivation to kill him, as a kind of self defense.
As for the scenes with Leonard and his wife--showing him pinching her hip playfully and then giving her an insulin shot in an alternate take--I believe they were "what if's" inspired by Teddy's conniving.
Whether or not Teddy or any other character in the movie committed the murder, I believe it happened and Teddy's taking advantage of it. The other explanation is that Leonard is a serial killer, inventing elaborate rationalizations for his murders. Leonard is cold and unsympathetic, but he seems too befuddled throughout most of the movie to pull that sort of thing off.
Now I want to see it again.
yeah, the scene i'm thinking of with his wife at the end is not the one you mention. they are lying (asleep?) in bed and you can see his tatooes across his chest. pretty positive it was her.