A New Jersey inmate dubbed the “Torso Killer” pleaded guilty to a 1968 slaying near New York City and admitted to four other homicides, prosecutors said Monday.

Richard Cottingham — believed to be one of America’s most prolific serial killers — admitted to strangling 23-year-old Diane Cusick on Feb. 15, 1968, at the Green Acres Mall in Nassau County, officials said.

In addition to Cusick’s case, he also confessed to four other Long Island slayings, officials said.

“Today is one of the most emotional days we’ve ever had in the Nassau County District Attorney’s Office,” District Attorney Anne Donnelly told reporters in Mineola.

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Cusick had left her job at a children’s dance school and then stopped at the mall to buy a pair of dance shoes when the New Hyde Park woman was strangled by Cottingham, authorities said.

Read more: NBC