A man being held in Texas has confessed to the killings of as many as 90 people over the past four decades.
Investigators in Louisiana and Georgia confirmed they were able to close four unsolved murder cases after Samuel Little, 78, who is already serving a life sentence for three murders in California, claimed to reveal all to officers.
According to a police memo, officers said the man provided details on two killings in Houma, Louisiana, "that only the murderer would have known".
The confessions related to Dorothy Richard, 59, who was found dead in 1982, and Daisy McGuire, 40, whose body was found in 1996. They were both strangled.
Little confessed to other murders in Louisiana, which police are still investigating, according to the memo.
Authorities in Georgia have also closed decades-old cases of two women who were killed and dumped in back gardens in the city of Macon following the confessions.
Bibb County Sheriff's Office said one victim was killed in 1977 and the other in 1982.
The earlier victim was never identified but her skeletal remains were found at the edge of some woods in a local back garden.
The 1982 case involved Fredonia Smith, who was found strangled to death.
Officers said Little was able to give them specific details and information which linked him to both killings. The Smith family has been notified about the latest development.
Of the 90 murders across the country, investigators have already been able to corroborate about a third, according to a Texas prosecutor.
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If the claims in Little's confessions prove true, it would make him one of the most prolific killers in US history.
Ted Bundy admitted to 30 killings between 1974 and 1978 and John Wayne Gacy killed at least 33 boys and young men in the 1970s.