NEW YORK (NewsNation) — The daughter and granddaughter of two women who were slain by a convicted serial killer and rapist are now working to secure more confessions from him.

Richard Cottingham, also known as “The Torso Killer” and “The Times Square Killer,” killed at least 12 young women and girls in New York and New Jersey between 1967 and 1980. Some historians believe he may have killed as many as 100 women.

One of those women, Deedeh Goodarzi, was mutilated and burned to death by Cottingham in 1979 at a hotel in Manhattan. Her biological daughter, Jennifer Weiss, was the first family member of a victim to deal extensively with Cottingham and to meet him personally inside prison after he was convicted of five murders in the 1980s. He is currently serving a life sentence.

Weiss has written notes to Cottingham while he is serving time for her mother’s murder.

“I make him feel comfortable so he can confess to me and tell me things he’s told nobody else,” Weiss said.

Weiss worked with investigators to convince Cottingham to plead guilty to a double homicide from 1974, the drowning murders of teen friends Mary Ann Pryor and Lorraine Kelly. 

Weiss isn’t the only one trying to get information out of the 75-year-old killer.

Sonia Ruiz-McGraw believes Cottingham also killed her grandmother, Lorraine Montalvo McGraw, in 1970.

“He didn’t say the words, ‘I killed your grandmother.’” Ruiz-McGraw told NewsNation affiliate WPIX. “He did say to me that he knew what happened to her.”

Lorraine Montalvo McGraw’s daughter — Sonia’s mother — was just 9 years old when her mom was killed, and she has never been the same.

“She absolutely just doesn’t know how to deal with it to this day,” Ruiz-McGraw said. “I know the toll that it took on my mother’s mental and emotional stability.”

Ruiz-McGraw visited the site where her grandmother’s body was found in South Nyack, New York, along with Dr. Peter Vronsky, a forensic historian from Canada who has written four books about serial killers. Vronsky has also worked extensively with Weiss.

Vronsky believes Cottingham may have killed as many as 100 women during a 13-year period from the late 1960s to 1980 when he was caught.

“You talk 100 victims? That’s one victim every six weeks,” Vronsky said.