A murder suspect linked to four deaths in Northern California strangled his girlfriend while being pursued by police at speeds of around 100 mph on a blown-out tire last week before being shot and killed by officers, authorities said Wednesday.

Cindy Tran was alive when the pursuit of Efren Valdemoro, 38, began around 8 p.m. on Aug. 31, California Highway Patrol Sgt. Trent Cross said. Valdemoro was driving Tran's car.

A co-worker who called Tran around that time said she could hear Tran yelling and sirens in the background before the call was disconnected.

A CHP officer found Tran's cold, lifeless body in the passenger seat of Tran's car when the pursuit ended about an hour later in Richmond, on the eastern shore of San Francisco Bay, Cross said. That information and autopsy results led investigators to believe Valdemoro killed Tran during the chase's early stages, Cross added.

Officers in pursuit saw no sign Tran, 46, was being attacked in the car, Cross said.

"It was dark, and they were behind the vehicle," Cross said. "They could see there were two occupants, but they didn't see any wild movement or anything like that."

Cross said authorities are not releasing details on the type of "instrument" used to strangle Tran. Pleasant Hill police officers who initiated the pursuit shot out the left rear tire of Tran's car before the pursuit began.

Valdemoro was later shot and killed by CHP officers inside a market in a strip mall when authorities said he grabbed two meat cleavers and lunged at them.

Valdemoro was a suspect in the beating death of Tran's housemate, Ricardo Sales, 73. Sales was found Aug. 28 in a Hercules home.

Police believe Sales' son, Frederick Sales, 35, may also have been killed by Valdemoro. Investigators and volunteers have spent nearly a week combing through a Contra Costa County landfill for signs of his body.

Valdemoro has also been linked to the bodies of Segundina Allen, 63, and Macaria Smart, 60, which were discovered at Allen's Vallejo home. Valdemoro lived with Allen and her husband, Charles Rittenhouse off and on for about 10 years.

Authorities arrested Rittenhouse, 72, last week after also discovering explosives at the home. Rittenhouse pleaded not guilty to explosives charges.

Rittenhouse was home when detectives found the bodies on Aug. 31 and has been questioned in the women's deaths. But Solano County prosecutors on Wednesday agreed to lower his bail from $2 million to $25,000, saying they didn't expect to file additional charges against him.

Rittenhouse's lawyer, Leslie Prince, expected her client to be released from jail Wednesday.

Deputy District Attorney Mike Mullins said Wednesday investigators are still examining all the evidence and haven't ruled anything out.

"All options are still open at this time," Mullins said. "We are still trying to figure everything out."