"It's not an accident. It's not a suicide," Capt. Frank Merriman told the Los Angeles Times in a story for Friday editions. "Phil Spector shot her."
No immediate decision was expected on whether criminal charges would be filed, said Sandi Gibbons, a spokeswoman for the district attorney's office.
Spector, whose "wall of sound" recording technique transformed 1960s pop music, was arrested Feb. 3 for investigation of murder after the body of 40-year-old Lana Clarkson was found in the foyer of his hilltop Alhambra mansion. He was released after posting $1 million bail.
Spector, 62, suggested in an Esquire magazine interview in July that Clarkson, an actress and hostess at the House of Blues, may have shot herself, but sheriff's investigators said in March that they discounted suicide.
A member of the Rock and Roll Hall of Fame, Spector has worked with such artists as the Beatles, Ramones, Shirelles and Ronettes, and has produced such pop music classics as "Da Doo Ron Ron," "Then He Kissed Me," and "To Know Him is to Love Him."