Robert Charles Browne
Robert Charles Browne was jailed for the murder of a young girl, Heather Dawn Church. While in prison he claimed to have killed 48 between 1970 and 1995 people across the US, which would make him one of the worst serial killers in US history.The killings allegedly took place across nine US states.
Investigators have so far been able to corroborate Browne's claims in six of the murders, a police official said.
Browne's confessions came after several years of correspondence and interviews between him and volunteer investigators following up unsolved murder cases.
A former truck painter, Gary Ridgway, pleaded guilty in 2003 to killing 48 women - crimes that earned him the nickname, the Green River Killer.
Browne appeared on Thursday in an El Paso court to plead guilty to the murder of Rocio Sperry, whom he said he strangled in 1987.
Browne said he started killing by murdering a soldier in South Korea in the early 1970s but police say this has not been verified.
Browne reportedly first came to the attention of the police was when he was questioned over the murder of Heather Dawn Church, who went missing in 1991 and whose skeletal remains were found in a ravine.