No point. As you say, it could still be easily faked.
After mulling it over, I think I believe him. He hinted at it early, which lends some veracity to his claim (or he just had this plan from the game's beginning), and revealed very quickly once slightly pressured (which is kind of odd, but generally mafia prefer to play it safe and only fake roleclaims when necessary).
But it would be easy to construct a plausible line of reasoning showing him to be lying as well, so this does no more than hint at his innocence, not prove it. Zfetch is still relatively null, and his roleclaim in and of itself doesn't prove innocence or guilt.