Douglas Culbreth, 73, of Upper Roxborough, a retired Philadelphia police detective who investigated the 1981 fatal shooting of Officer Daniel Faulkner by Mumia Abu-Jamal and remained a firm believer in Abu-Jamal's guilt, died Friday, Dec. 26.

He suffered an apparent heart attack, said Aisha Perry, a family friend. He had fallen ill at home and was taken to Roxborough Memorial Hospital, where he was pronounced dead.

Mr. Culbreth, a Vietnam War veteran, also served as an investigator for the Defender Association of Philadelphia, where he worked for 18 years until his death.

Morris Tolbert, a longtime friend, said Mr. Culbreth was a "straitlaced, straightforward" man who was "really frustrated" by the advocacy of people contending that Abu-Jamal was innocent.

"He would get upset when people said [Abu-Jamal] didn't do it," Perry said. "He said there was no doubt Wesley Cook - Mumia Abu-Jamal - killed that officer."

Mr. Culbreth grew up in North Philadelphia and graduated in 1959 from Dobbins Vocational High School.

He served in the Army from 1961 to 1965 and was assigned to the 101st Airborne Division.

He joined the Philadelphia Police Department in 1966 and eventually became a homicide detective. In that capacity, he worked on the Faulkner case and also on the 1993 robbery-murders of brothers Russell and Stacy Krass in their Frankford Avenue clothing store.

Mr. Culbreth retired in 1996 and then joined the public defender's office.

He was an avid genealogist, researching his family's roots as well as many others, especially African American veterans. He was an active member of Canaan Baptist Church.

Mr. Culbreth is survived by his wife of 31 years, Hazel; sons Derek and Stacy; and daughter Rashida. A son, Devin, died in a 2003 car accident.

Funeral services were pending.