serial killer already serving life for murdering nearly a dozen women decades ago has admitted to an additional five slayings.

The Associated Press reports Richard Cottingham, who’s best known as the “Torso Killer,” pleaded guilty to second-degree murder in connection with the 1968 rape and killing of Diane Cusick. Cottingham also admitted to the slayings of four other women in Long Island’s Nassau County in 1972 and 1973.

Sentenced to 25 years to life behind bars for Cusick’s slaying, Cottingham received immunity for the other four murders due to a plea agreement. 

“Today is one is one the most emotional days we’ve ever had the Nassau County District Attorney’s Office,” District Attorney Anne Donnelly told reporters. “In the case of Diane Cusick, her family has waited nearly 55 years for someone to be held accountable for her death.”

“It was only through advances in DNA technology that the NCDA and our partners at the Nassau County Police Department, could solve this 54-year-old cold case and identify a suspect in Ms. Cusick’s tragic death,” Donnelly added. “We make a promise to her surviving daughter today: we will bring her mother’s killer to justice.”

Believed to be one of America’s most prolific serial killers, Cottingham has claimed he’s responsible for up to 100 homicides. The 76-year-old has been imprisoned since 1980, following his convictions in 11 other killings.

At the time of Cottingham’s arrest in 1980, he was married with three children, while working as a computer programmer for a health insurance company in New York.