I've never seen the documentary but you intrigued me, so did some digging. Looks like the editor of the Staircase became "romantically involved" with Peterson. Such a freakin' socio. Just like many other historical killers (Bundy, anybody?), charming enough to bang a lot of people who should know better. There was a "Peterson" on the west slope, named Michael Blagg. He got a retrial on a technicality, also tried a long-shot defense explanation trying to assert it was a different serial killer who happened to be in the area.
He failed. Guilty 2x.