Bill Ferguson is a driven man. A real estate broker, nothing in his life ever prepared him for what he is doing now: trying to solve a 10-year-old murder. "I started going to the crime scene within a week of the arrest... I'd go down at 1:30 [a.m.],... (more) stay down 'til 3 o'clock," Ferguson tells "48 Hours Mystery" correspondent Erin Moriarty. "I would sit in different spots of the whole crime scene, from different angles. I'd do it every Halloween for sure." Ferguson says he's gone down to the crime scene "40, 50 [times] at least." "What did you know about investigations before this?" asks Moriarty. "Well, I used to watch 'Perry Mason,'" he replies. One thing Ferguson knows for sure, he says, is that his 26-year-old son, Ryan, is innocent. "I wanna be exonerated," Ryan tells Moriarty. "I want everyone to know that I have absolutely nothin' to do with this case." Ryan is Bill Ferguson's only son. "We've always been close. Really, really close," Ferguson says. "He never gave us trouble at all." Ryan had just turned 21 in 2005, when he was convicted and sentenced to 40 years. The key witness against him is his high school friend, Chuck Erickson, who told the court that he and Ryan robbed and murdered 48-year-old Kent Heitholt.