Retrograde Analysis

There is a good book called the Flander's Panel, where an old painting depicts the Duke of Ostenburg playing chess against one of his knights.  The Duke had been murdered and clever historians figure out that the painting is a clue as to who did it.  The position on the board symbolically represents the Duke alongside potential suspects, and by trying to figure out the previous moves in that chess game, they uncover a clue as to who murdered the Duke.

In this position, all you need to know is that black made the last move.  You must figure out exactly what that move was, and also what white's move was prior to it...nothing more.  There is only one possibility.  I assume the brains here will easily figure it out, but if after too long there isn't a solution, I will post it as cleverly revealed in the book's pages.

 On a side note, if you like this kind of puzzle, and would like to read a good mystery/thriller with a snazzy chess game at it's core, read The Flander's Panel by Arturo Perez-Reverte.