Two weeks after Tiburon resident Joan Rosenthal was found shot to death outside her home, police are still working to determine a motive for the murder, the city’s first in a decade.Rosenthal’s body was found outside her house at 647 Hilary Drive at about 9:40 a.m. on Sept. 22.”There are a wide variety of possible motives, which leads to a wide variety of possible suspects,” San Rafael police spokeswoman Margo Rohrbacher said today. Rohrbacher is assisting Tiburon police in the case. Detectives have questioned guests who attended a party held at a home adjacent to Rosenthal’s the night before her body was found but no leads were developed, Rohrbacher said.Investigators have also searched Avenida Miraflores, which runs perpendicular to Hilary Drive, using specially trained search dogs to try to determine the shooter’s exit route, Rohrbacher said. However, it is still unclear whether the shooter fled on foot or in a car.In a separate case, Belvedere police and San Rafael police have been investigating a burglary suspect who lives in the Del Mar neighborhood, where Rosenthal was killed. A search warrant was served last week and investigators have determined that the suspect is not connected to the killing, Rohrbacher said.