A 78-year-old man might be responsible for as many as 90 unsolved murders across the US, Texan authorities say.

Samuel Little was handed three life sentences in 2014 after being convicted of strangling three Californian women in the late 1980s.

This year he was charged with the 1994 murder of a Texas woman and was extradited from California in September to assist with investigations.

Since then, Little has claimed to be involved in roughly 90 killings since the 1970s, Ector County District Attorney Bobby Bland said.

"They're able to match up over 30 cases so far," Mr Bland said.

Little, who sometimes went by the name of Samuel McDowell, looks set to become the worst serial killer in the history of the US.

If his confession proves to be true, his death tally would surpass that of Ted Bundy, who admitted to the rape and murder of 30 women between 1974 and 1978.

He would also eclipse John Wayne Gacy, who sexually assaulted, tortured and killed at least 33 boys and young men between 1972 and 1978.

Little would prey on "troubled" women, targeting drug addicts and prostitutes, first taking them down with a knockout punch.

He would then strangle them while masturbating, before dumping their bodies and skipping town.

Authorities first convicted him for the Californian strangulations after matching his DNA with semen and samples found on the victims' clothing, NBC Los Angeles reported in 2014.

But now more grisly details of his killings have come to light. (ABC News)