There was some speculation that they may have retrieved a cigarette butt. This was back when they were back on the bridge several days after the girls were found.
I remember that. OK... so the Journal and Courier has a good online article, where Sgt Riley says he anticipates answers about DN's involvement in Abby and Libby's case next week. That they are getting his DNA samples and that they will be matched to evidence collected at the crime scene ( that answers that question, thankfully.) The article also states that Colorado FBI will be questioning DN, but that Indiana FBI might travel there if the need arises. Also Riley says he is a person of interest in the same way anyone would be until they are either cleared or named as a suspect.