Samuel Little, the country's most prolific serial killer who confessed to more than 90 slayings, has died. He was 80.

The California Department of Corrections and Rehabilitation said he died early Wednesday morning at a hospital. The Los Angeles County medical examiner is expected to determine an official cause of death.

Little spent weeks in interviews with Texas Ranger James Holland, divulging details about the killings and offering corroborating evidence. He also drew portraits of more than 30 of the victims, describing where he met them, what they were wearing, how he killed them and where he hid their bodies.

He told investigators that he strangled all of them. His first killing was in 1970 and the last in 2005. The crimes took place in 19 states, with most of his victims in California and Florida.

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The FBI named Little "the most prolific serial killer in U.S. history" last year, and its analysts believe all of his confessions are credible, although some of the deaths originally were ruled accidents or overdoses. Some victims were never found.

He was a former boxer, and investigators said they believe he knocked out his victims with a punch before strangling them while masturbating. The victims were mostly prostitutes, drug addicts and women living on the margins of society. At least one was transgender.

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Prior to getting caught for the slayings, he was in and out of prison. California authorities said he served four years for assault with a deadly weapon in the mid-1980s and was given probation in 2012 for possession of a controlled substance.

DNA samples taken while he was in custody linked him to three unsolved homicide cases dating back to the 1980s. In 2014, he was sentenced to three life sentences without parole.

The FBI posted some of Little’s confessions in his own words to YouTube. In 1984, he said he met a 25-year-old "hippie"-looking woman outside a strip club who asked him for a ride from Cincinnati to Miami.

He drove her to Kentucky and killed her there, leaving the body on a hill.

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"I seen a little short road going up the hill, and up top, there was vegetation – wasn’t no houses or nothing," he confessed on video. "And so I pulled up in there and concealed the car in that little vegetation up there."

In an interview in 2018 with The Cut, a web-based subsidiary of New York magazine, he said that killing his victims "felt like heaven."

The Associated Press contributed to this report.