Authorities are offering a $25,000 reward to try to jump-start the investigation into the killing of a 75-year-old woman in the affluent city of Tiburon, north of San Francisco.
Joan Rosenthal was shot once in the head outside her home and was found by a friend on Sept. 22, 2009.
Authorities on Tuesday announced a $25,000 reward for information leading to a conviction in the case.
Police say the killing remains a mystery. There were no signs of a robbery, and investigators have not been able to identify another possible motive.
Tiburon Police Chief Michael Cronin said investigators have spent nearly 4,000 hours on the case and interviewed more than 100 people.
Rosenthal's death was only the fourth homicide in Tiburon in 40 years.
Copyright AP - Associated Press
