If Samuel Little truly killed 93 people, he'd be the most prolific serial killer in American history.

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A man who is possibly the most prolific known serial killer in American history has pleaded guilty to four more murders.

Samuel Little, 79, told federal authorities last year he'd committed nearly 100 murders across the country from 1970 to 2005. He'd previously been convicted in 2014 of strangling three women in Los Angeles during the 1980s and was serving a life sentence, but confessed to the other murders in exchange for a prison transfer, according to NBC News. Since then, authorities have been working to verify those claims and identify the victims.

Last week, Little pleaded guilty to four more murders in Ohio: two women in Cincinnati — Anna Stewart, 32, and an unnamed woman — and two in Cleveland — Mary Jo Peyton, 21, in 1984 and Rose Evans, 32, in 1991 — the Chicago Tribune reports.

This now brings the killers’ confirmed victims up to 60. In all, Little has claimed he killed 93 different women in 14 different states.

Little pleaded guilty over Skype from California, where he is currently serving multiple life sentences. Now, he has a few more life sentences to serve: two consecutive terms of 15 years to life for the Cincinnati murders and a minimum of 40 years for the Cleveland slayings.

Prosecutors said Little didn’t rape the women but that he killed them for sexual gratification.

"His bare hands on the bare necks, that's what actually got him sexually aroused and that's why he did this," Mark Piepmeier, a Hamilton County prosecutor said, according to the Chicago Tribune. "It wasn't for any other reason."

Little’s attorney Timothy McKenna told the judge in Cincinnati that his client’s health is failing and that Little wants to help investigators close cases to bring closure to his victims’ families.

“Little chose to kill marginalized and vulnerable women who were often involved in prostitution and addicted to drugs,” the FBI said last year. “Their bodies sometimes went unidentified and their deaths uninvestigated."

Last year the FBI released a map showing who Little claimed to have killed and where, and earlier this year, Little created portraits of his unidentified victims.