You must be referring to Linda Kasabian, who went along on both nights, witnessed at least 2 of the murders at the Tate house but didn't actually kill anyone herself. She was granted full immunity for her testimony against Manson and the others and never served a day in prison. (Did anyone see her on Larry King last month?)

Unfair? Sharon Tate's sister sure thinks so...however Bugliosi has stated that without Kasabian the prosecution would've had no case. I think it was as fair a trade as they could get.