In Chapter twenty-six "The Cave" Dumbledore and Harry Potter discover that Voldemort's Horcrux has been stolen and at the end of two chapters later Harry reads a note written by an R.A.B. admitting to taking this Horcrux. Well, many in the Harry Potter fan world have riddled about who this R.A.B. is. My guess is that first of all this was the very cave to which Riddle had taken Benson and Bishop. One or both of them must have then returned there later and thwarted Voldemort's devices by taking the Horcrux. The initials of the thief point to Amy Bishop with the 'R' standing for some title.
August 2007 - Well, after having read "Harry Potter and the Deathly Hallows" it seems Benson and Bishop play no role what so ever in the last Potter novel. Too bad; Benson and Bishop would've been glad to have defeated of Voldemort.