Police have linked more than 60 killings in at least 14 states to a 79-year-old inmate who may be the most prolific serial killer in US history, a Texas prosecutor said.

Ector County District Attorney Bobby Bland said that Samuel Little continues to cooperate with investigators from around the country who interrogate him in prison about cold case killings dating back to the 1970s.

Little was convicted of killing three Los Angeles area women and pleaded guilty to killing a Texas woman. He is serving life sentences in a California prison.

Serial Killer Investigations-Cold CasesSamuel Little is said to be in failing health (Mark Rogers/Odessa American via AP,)

Little, who lived a nomadic lifestyle, claims to have killed at least 90 women as he criss-crossed the country over the years. Mr Bland said Little is in failing health and “he’s determined to make sure that his victims are found”.

Gary Ridgway, the so-called Green River Killer, pleaded guilty to killing 49 women and girls, making him the most prolific serial killer in US history in terms of confirmed murders, though he said he killed 71.