Nancy Grace We're 'Investigating' the Mystery Fart

10/4/2011 5:25 PM PDT

Nancy Grace -- We're 'Investigating' the Mystery Fart

-- Nancy Grace claims she's been FRAMED in the "Dancing with the Stars" fart mystery ... and tells TMZ an "investigation" is underway to find out who REALLY dealt it.
Grace -- who was doing a post-dance interview on the show last night when someone let it rip -- tells us, "As an ear witness on the scene, I can absolutely exonerate Tristan, myself and Brooke."

She adds, "However, the rest of the cast -- seated just inches away -- all remain under grave suspicion.  The investigation continues."