to parole out. somebody held the grudge, and got out and wanted him. reporter: even though investigators were convinced he was murdered because of his job as a prosecutor they doesn t stop there. we have to interview friends and family members and associates. reporter: mark was a tea tottler and he did not have a wife or kids. there was nothing there, he loved his mother who lived in dallas, he spent time taking care of her and taking her to dinner. reporter: all the initial checks in to his professional and personal life was not panning in. frustration was setting in. the cases get harder to solve after the first 48 hours. two full days in, mark s murder had reached that cross-road and investigators were searching desperately for a break. understands tell us tonight there s simply no promising leads in the case right now. this murder is turning in to a who done it.