<P> Stone became Executive Assistant DA in 1985 after convicting con artist and murderer Philip Swann, who years later enters a civil suit against Stone when the validity of the conviction is called into question . (Swann is ultimately found guilty, however, and sent back to prison .) Stone's assistants have been Paul Robinette and Claire Kincaid . </P> <P> A strict, unyielding boss, Stone can be very difficult to work with; in the pilot episode, Sergeant Max Greevey and Detective Mike Logan, intimate that Stone "eats ADAs for lunch ." Nevertheless, Stone is usually rather soft - spoken, and is fond of using harmless words like "sir" to convey his contempt for the people he prosecutes . </P> <P> Stone makes his last appearance in the show in the episode "Old Friends," the final episode of season four . The episode portrays a racketeering case in which the main witness (portrayed by Allison Janney), whose testimony Stone had secured by threatening to send her to prison, is murdered by the Russian Mafia . He feels responsible for her death and resigns from the DA's office . He is succeeded by Jack McCoy as Executive ADA . </P> <P> Stone is mentioned in the 1996 episode "Custody" as a possible witness against a judge . When his former assistant Paul Robinette, now a defense attorney, wants a judge to recuse himself for past comments showing bias against drug addicts and support for forced sterilization, Robinette threatens to subpoena Stone to testify about the comments, which both he and Stone heard the judge make . Upon hearing of the threat, Schiff informs McCoy that Stone "is travelling in Europe, not available to testify at any hearing ." However, the judge by this time has already declared himself "unavailable" to hear the case . </P>

What happened to ben stone on law & order special victims unit
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