A convicted serial killer on death row in California has been linked to the cold case killing of a pregnant woman in 1977 after a photograph of the victim was found among a collection in his possession.

Rodney Alcala, known as the "Dating Game Killer" because of an appearance on a US game show in 1978, has already been convicted of five murders and confessed to two more and could have killed up to 130, police believe.

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The photograph has been identified as Christine Ruth Thornton, from San Antonio, Texas. Her remains were discovered by a rancher in Granger, southwest Wyoming in 1982 but weren't identified as being Ms Thornton until 2015. Investigators believe Alcala met the pregnant woman on a road trip, killing her and hiding her body (San Jose Mercury). He appeared on the TV show the next year, being chosen to go on a date with a contestant who changed her mind after the programme.

After Alcala, now 73, was convicted of the murder and sexual assault of four women and a 12-year-old girl in 2010, hundreds of photographs mostly of women found in Alcala's Seattle storage locker in 1979 were published online (CBS). Many of those photographed have been identified and found unharmed but a number remain unidentified and unaccounted for.

One was of Thornton, 28 when she disappeared, taken in the same area of Granger where her body was found. Thornton's sister recognised her picture and contacted investigators to submit her DNA. A match was found in 2015. Wyoming police were able to recognise the location in the photograph as that where Thornton's body was found decades earlier.

Alcala has been sentenced to death and is at California's Corcoran State Prison. On Tuesday (20 September) he was charged with Thornton's murder. It is unclear when he will be sent to Wyoming to face additional murder charges. When investigators showed him a picture of Ms Thornton he said he took it. Asked if she was alive when he left her he said: "She was alive before I left her."