Jinmei Chen, 45, was found murdered on the 500 block of East Valley Boulevard around 5 p.m.
Authorities said two of the victim's friends came to check on her because they hadn't heard from her for several days.
Police say there is no sign of any forced entry, indicating Chen may have known her attackers.
The victim lived alone in what, nearby residents say, is normally a pretty quite neighborhood.
Lt. John Corina of the Los Angeles County Sheriff's Department says the homicide is unusual.
"I don't think we've had a homicide for at least a couple of years," said Corina.
The killing has sparked concern in the San Gabriel community, as neighbors worry the brutal incident was random.
"It scares us, because if it was a random killing, we could be next," said an unidentified neighbor.
"There's four homicides, including this one, since 2007," said San Gabriel City Councilman Chin Ho Liao. "So San Gabriel is a fairly safe city."
An autopsy report is scheduled to reveal when Chen was killed.
The motive for the slaying remains unknown. Authorities say they have no suspects nor anyone in custody over the homicide but that the investigation is ongoing.
Anyone with information about this incident was asked to contact the Los Angeles County Sheriff's Department's Homicide Bureau at (323) 890-5500.