CINCINNATI -- A man who claims he has killed more than 90 women across the country pleaded guilty Friday to murdering four women in Ohio.

Samuel Little appeared via Skype from the California state prison where he's serving multiple life sentences. He admitted in separate hearings that he killed two women in Cincinnati and two in Cleveland.

Little is possibly the most prolific serial killer in U.S. history, surpassing others such as John Wayne Gacy, Ted Bundy and Gary Ridgway, the Green River Killer.

He was convicted in California of three slayings in 2013 and pleaded guilty to another killing last year in Texas.

Authorities have said they've confirmed at least 60 of the 93 slayings he says he committed in 14 states while he crisscrossed the country for decades.

Mark Piepmeier, a Hamilton County prosecutor, said Little told investigators he didn't kidnap or rape the women, and that he targeted women he didn't think would be missed right away. Little said he got sexual gratification from strangling women, the prosecutor told the court.

"His bare hands on the bare necks, that's what actually got him sexually aroused and that's why he did this," Piepmeier said. "It wasn't for any other reason."

In Cincinnati, Hamilton County Judge Melba Marsh asked the 79-year-old man a series of questions about giving up his rights to trial that Little answered affirmatively, sometimes with, "Yes, ma'am."

Raising her voice when Little had trouble hearing her, Marsh then sentenced him to two consecutive terms of 15 years to life.

Defence attorney Timothy McKenna of Cincinnati told the judge that at this stage in his life, Little wants to help police identify his victims and close cold cases. He also said Little is in failing health.

McKenna and Piepmeier flanked Little at a table in the California prison while Marsh conducted the hearing from Cincinnati, in the Hamilton County law library. Franklin County Prosecutor Ron O'Brien joined Hamilton County authorities in Cincinnati.

Little admitted to the 1981 murder of 32-year-old Anna Stewart, last seen alive in Cincinnati. Her body was dumped in Grove City, near Columbus. He also confessed to a second Cincinnati murder, of a woman who remains unidentified.

Just hours after being sentenced in Cincinnati, Little pleaded guilty and was sentenced via Skype for the slayings of two women in Cleveland.

Authorities said Little strangled to death Mary Jo Peyton, 21, in 1984 and Rose Evans, 32, in 1991.

Cuyahoga County Judge John Russo sentenced Little in Cleveland to a minimum of 40 years in prison to be served after the sentences he's received in Texas, California and Cincinnati.

Russo said the pain and suffering Little has caused the families of all the slain women "is not describable."

An attorney for Little read a statement in the Cuyahoga County hearing saying Little "thoroughly apologizes" for the slayings and wants to bring closure to the women's families.

Authorities in the Cleveland area are still investigating a third possible murder by Little there.