On a May morning in 1972, the body of Mary Beth Heinz, 21, was found floating face down in a muddy creek on Long Island. An autopsy determined that she had been strangled.
Three months later, the body of Laverne Moye, a 23-year-old mother of two, was found in the same creek. She, too, had been strangled. In July 1973, Sheila Heiman’s husband returned to the family’s Long Island home to find her bludgeoned to death. The couple’s children were at summer camp at the time. Five months after that, Maria Emerita Rosado Nieves, 18, was found dead in an overgrown area at Jones Beach, another strangling victim.
For five decades, the cases went unsolved. That changed on Monday, when a man already in prison after being convicted in the serial slayings years ago of several other women in New York and New Jersey admitted to killing Ms. Heinz, Ms. Moye, Ms. Heiman and Ms. Nieves.
The admissions came as the man, Richard Cottingham, pleaded guilty to murder in the killing of a fifth woman, Diane Cusick, a 23-year-old dance instructor who was found strangled in her car at a Long Island mall on a February evening in 1968.
Anne T. Donnelly, the Nassau County, N.Y., district attorney, said in a statement that Mr. Cottingham, 76, had “caused irreparable harm to so many people and so many families” and had “assaulted and brutally murdered” his victims “to satisfy his craven desires.”
“Thankfully,” she added. “He will spend the rest of his life in prison, where he belongs.”
As part of an agreement with Ms. Donnelly’s office, Mr. Cottingham will not be prosecuted for the four other Nassau County killings to which he admitted under oath on Monday. He was sentenced to 25 years to life in prison for the murder of Ms. Cusick.
“We are confident that he killed all five of these women,” Ms. Donnelly said at an emotional news conference after the hearing.
Mr. Cottingham’s lawyer did not immediately respond to messages seeking comment.
Mr. Cottingham is known as the Torso Killer because he cut the heads and hands off some his victims. He claims to have killed more than 100 women, and although investigators believe he has other victims, they have yet to link him to that many slayings.
Still, before Monday he had been convicted of or admitted under oath to at least 11 killings. He appeared at the Nassau County proceeding via video feed from a state prison in New Jersey where he is serving multiple life sentences.
Mr. Cottingham was charged in Ms. Cusick’s murder in June after DNA collected from the crime scene more than 50 years earlier matched his profile in a federal database.
The breakthrough, Ms. Donnelly said, led the Nassau County authorities to revisit the unsolved murders of women in the area from 1967 to 1980, the period when Mr. Cottingham was on his killing spree in and around New York City.
In interviews with Mr. Cottingham, Ms. Donnelly added, investigators were careful to hold back key information about the crimes.
“We did not want a scenario where a serial killer claimed credit for a murder he did not commit,” she said.
In the four cases he admitted to on Monday, she said, he knew details of the crimes that only the true killer would know.
Mr. Cottingham, a married father of three who worked as computer operator in Manhattan and lived in Lodi, N.J., was first convicted of murder in the early 1980s. Telling his wife that he worked at night, he rented an apartment in Midtown Manhattan and preyed on prostitutes who worked in the Times Square area, a seedy section of the city at the time.
In discussing Mr. Cottingham’s admissions on Monday, Ms. Donnelly emphasized that it was a “misperception” that he had solely targeted sex workers.
“Richard Cottingham killed who he wanted, when he wanted because he’s a serial killer,” she said. “That is what he is.”
Law enforcement authorities were accompanied at the news conference by several of Mr. Cottingham’s victims’ family members, including John Moye, Ms. Moye’s son. Like the other relatives in attendance, he expressed gratitude that his mother’s killer was finally being held to account.
“There’s been some dark days,” Mr. Moye said, “but today the sun shines brightly because justice has been served.”
Kirsten Noyes contributed research.