A convicted serial killer on California death row for murdering a dozen people in the 1980s and ’90s confessed to the 1986 murder of a 19-year-old woman in Los Angeles County, the police announced on Tuesday.

William Lester Suff, 70, confessed in May 2022 to stabbing Cathy Small to death and dumping her body on a South Pasadena, Calif., cul-de-sac, where her body was discovered by police on Feb. 22, 1986, the Los Angeles County Sheriff’s Department announced at a news conference on Tuesday. Why the announcement came more than two years after the confession was not clear.

Ms. Small’s body was found in the morning wearing a nightgown, and she died from multiple stab wounds and strangulation, Lt. Patricia Thomas said.

Ms. Small’s body was identified three days later by a man who had read about the killing in the news and had called detectives to say he was concerned that the victim could be his roommate.

He told detectives that she had worked as a prostitute in the Lake Elsinore area and had lived at his house for a few months, Lieutenant Thomas said.

The man said that Ms. Small left their house on the night of Feb. 21, 1986 wearing a nightgown. Ms. Small, he added, told him that a man named Bill was paying her $50 to join him on a drive to Los Angeles.