A death row inmate's case is getting a fresh look after more than three decades. But evidence is missing and some witnesses are dead.

An unusual investigation quietly taking place in California could lead to a resolution of the most hotly debated death row cases in the country. Last May, Governor Gavin Newsom issued a rare executive order to launch an independent investigation into the case of Kevin Cooper, an inmate who was sentenced to death in 1985 for the murders of four people in Chino Hills, California. He has been on death row in San Quentin ever since. 

CBS News' "48 Hours" began reporting on the case in 2000 after receiving several letters from Cooper, claiming his innocence and asking the show to investigate: "I Kevin Cooper am an innocent man, and I am on death row waiting to be murdered for something I didn't do!" 

The controversial case dates back to June 5, 1983. Doug and Peggy Ryen were found murdered in their home, along with their 10-year-old daughter Jessica, and a young neighbor, 11-year-old Christopher Hughes. It was an extraordinarily brutal crime: The victims had been stabbed 143 times with three different weapons. Somehow, the Ryen's 8-year-old son Josh, whose throat was slashed and skull fractured, managed to survive.