CASPER, Wyo. -- An imprisoned serial killer already sentenced to death in California has been charged in connection with the killing of a 28-year-old whose remains were found in southwest Wyoming in 1977.

Wyoming police charged Rodney Alcala on Tuesday with first-degree murder in connection with the death of Christine Ruth Thornton, the Orange County Register reported.

Investigators said they believe the now 73-year-old Alcala killed Thornton in Sweetwater County based on a photo that appears to show her on remote public land near Granger, close to where her remains were found. The photo was found while searching Alcala's possessions during a previous investigation.

Alcala is imprisoned in California's Corcoran State Prison. He has been connected to six murders in two states, though authorities estimate he may have killed up to 130 people across the country.

Prosecutors say Alcala met and killed Thornton while on a road trip and buried her on a ranch, the Register reported.

Her body was uncovered by a rancher in 1982, but the alleged link to Alcala was not discovered for decades, the newspaper says.

Thornton was about six months pregnant at the time of her death, according to the warrant for his arrest.

It is unclear whether Alcala will be extradited to stand trial in Wyoming and what his plea might be, the Register said.

Authorities credit the charge for Thornton's murder, in part, to information provided by an investigation by the Huntington Beach Police Department.

The link to Alcala was established after the department in 2010 decided to release about 200 photographs taken by him to the public, hoping people who knew other possible victims would see them. "I had a gut feeling there were more out there," Huntington Beach police Detective Patrick Ellis told the newspaper.

Thornton's sister, Kathy Thornton, recognized the subject of one of the photographs as her sister in 2013, according to the Register.

Thornton is the first alleged victim linked to those photos, but Ellis said he believes there could be others.

Alcala has been in jail or prison since 1979, the Register reported.