SAN FRANCISCO — The FBI has joined the investigation into the killing of a retired schoolteacher in her home in the usually tranquil city of Hercules over the weekend.

Federal forensic investigators and police detectives searched the home of Susie Ko most of the day Monday, said Hercules police spokeswoman Connie Van Putten.

Ko, a mother of four adult children, was found dead on the floor of her home by neighbors who were called by her husband, Kelvin, when she failed to pick him up at Oakland International Airport late Friday.

A preliminary autopsy report showed that Ko, 55, died of stab wounds and blunt force trauma to the head, Van Putten said. No suspects have been identified.

"We did get some items that may be of evidentiary value, but we won't know for sure until they are processed by the county crime lab," Van Putten said.

Police were asking the public for help in locating the family's sky blue 2011 Subaru Outback with Idaho license plates, which was missing from the home. The car is the only item that appeared to be missing.

Investigators have fielded a number of calls about possible sightings of the car across Northern California. Police believe Ko's killer may have changed the plates on the car, Van Putten said.

"If someone sees a sky blue Subaru Outback and it seems suspicious to them, and they can safely get a license plate, we would really appreciate the license," Van Putten said.

Ko's children returned to Hercules to support their grieving father, and to encourage the public to help find the killer of their mother.

"We are just trying to surround him with love," Simon Ko, 29, said of his father.

Simon Ko remembered his mother, who taught elementary school in nearby Rodeo for more than 13 years and lived in Hercules for more than 30 years, as a "very high spirited, social and fun-loving person."

The family has set up a website for tips and information at

The homicide is the first in Hercules since 2010, Van Putten said.

The mostly residential community of upscale homes and quiet neighborhoods about 23 miles northeast of San Francisco has only seen five homicides in the past 12 years, she said.

"We think we have a safe city, Van Putten said. "We've had a few robberies and some burglaries, but as far as violent crime, we just haven't had that much."