NEW BEDFORD (CBS) – More than 30 years later it still remains a mystery. Eleven women vanished from the same area of New Bedford during March of 1988 and April of 1989.

Maureen Boyle wrote the book Shallow Graves about the investigation into the New Bedford highway killer.

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“You had remains of woman after woman found on two highways. Similar situations, similar backgrounds. All addicted to drugs – that was the unifying element,” Boyle said.

Author Maureen Boyle. (WBZ-TV)

Judy DeSantos said her sister Nancy Paiva was addicted to drugs. When she hadn’t heard from Paiva in a couple of weeks, DeSantos became worried.

“I knew something was wrong,” DeSantos told the I-Team. “I had such a bad feeling.”

Paiva, a 36-year-old mother, was last seen leaving a local bar. Her body was discovered three weeks later off of Interstate 195 in Dartmouth.

“Every time I go by there I’m always looking,” DeSantos said. “Somebody thought she was trash and could dispose of her so easily. It makes me angry.”

Eleven women who vanished in New Bedford from 1988-89 (WBZ-TV)

Nancy was the second victim of what became known as the New Bedford highway killer.

Boyle said Paiva’s case is what got things moving. Former New Bedford police detective Richard Ferreira and his partner investigated Paiva’s murder and connected her case to other missing women.

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Ferreira said they quickly learned, “I think we have a serial killer around here.”

When the killing spree ended, police found the bodies of nine of the women. While there were suspects, no one was ever charged.

“It’s the most difficult case I’ve ever investigated,” Ferreira said. “The hardest thing for me is the families particularly the families of the two girls that we never recovered the remains of. That really haunts me.”

Maureen Boyle’s book Shallow Graves. (WBZ-TV)

Boyle is haunted too, and dedicated her book in part “to the families of the lost still looking for an answer, still believing and hoping that whoever is responsible for the killings will one day be identified.”

Hope is all DeSantos and the other families say they have left. But they know ultimately time may rob them of justice.

DeSantos believes someone knows something, and she told the I-Team she made a promise to her sister “that I would never give up. And I won’t.”

Anyone with any information about the murders or the missing women is asked to contact the Bristol County District Attorney’s office.

A spokesperson for the Bristol County District Attorney released this statement:

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“We are utilizing the most up to date to technology in this case and several other cold cases from previous administrations. We have completed DNA testing in the case, which remains active and ongoing. We continue to pursue all leads and follow up on tips regularly. Our office’s Cold Case Unit has been publicly highlighting unsolved homicides from previous administrations, dating back several decades, and we will continue to do so.”

Cheryl Fiandaca