A Wonderful Find ...

[Crowza]

After the shot rang out that wounded Booth, Conger thought Booth had shot himself. Byron Baker disputed this, since he was watching Booth very carefully at the moment he was shot. Boston Corbett then reported to Lt. Dohetry that he was the one who shot Booth. As proof, he showed him the spent percussion cap and the empty chamber in his 1860 Colt.

Source: American Brutus (Michael Kauffman) - Chapter 15 (no exact page number, as I have the Kindle edition)

To offer a theory that Booth committed suicide, I'd say one would need to explain away all of evidence to the contrary. Not just that the shot was physically possible, but to explain the fresh spent percussion cap and the empty revolver chamber (not to mention, Baker's eyewitness account).

Further, it would have been better for the men involved to say that Booth killed himself, as I believe the standing orders from Stanton was to take him alive. Even though Corbett wasn't punished for shooting Booth, they all had no idea at the time that they wouldn't be.

IMHO, there is simply no written or physical evidence that supports the notion of Booth killing himself, just pure speculation.