d.a. mike mclelland had to bow out of the investigation. he and his co-workers were doing what they could, opening their files to investigators. >> everything anybody can think of, they're looking through it. >> checks into mark's personal background had gone nowhere. so the task force continued to look at his professional cases from 30 years ago to the week before. but it was slow going. how do you sift out, well, it couldn't have been this person, but maybe it was this person? >> first of all, you see if they're still locked up. you see where they are, their whereabouts. you see is there anything unusual or specific about a case that would give someone cause to have a grudge in. >> four weeks into the investigation, a tip came into the county crimestoppers anonymous tip line that looked like a big break. >> the tipster said that they'd been in a bar in a small town in kaufman and overheard two white males talking about the hasse killing and taking responsibility for it. >> the tip lacked the kind of detail that investigators needed to fol