ROCKFORD, Ill. (WTVO) — The 3000 block of Edelweiss Road was quiet and uneventful during the daylight hours of Dec. 4, 1979.

That all changed at 11:30 p.m., when two young girls who lived in a small duplex heard people fighting inside the adjoining apartment.

The girls knew the couple next door, a 23-year-old man named Willard Colwell and his fiancee, Rosemary Peterson, also 23. But, they soon noticed that Colwell’s car wasn’t at the duplex, but Rosemary’s was parked in her usual spot. Something wasn’t right.

As the ruckus continued, the girls knocked on the couple’s door and called out to Rosemary. They first heard a man shout that they “just had a fight.” Rosemary Peterson then screamed for help.

Entering the house, the girls were met with one of the bloodiest crime scenes ever investigated in Rockford, second perhaps only to the one left by Simon Peter Nelson, who in 1978 killed his six children with a knife and mallet inside their home.

Rosemary Peterson was found tied to a bedpost. She’d been stabbed multiple times and suffered a massive blow to the head. One of her hands was nearly cut off, presumably by one of the several kitchen knives or the machete found at the scene. She died the next day.

Colwell was at work at a local factory during the attack and has never been named a suspect. That has led to the theory that someone else was allowed into the apartment. There was no sign of forced entry, and Peterson’s friends all told police she’d never open the door for a stranger, especially at 11:30 p.m.

“The attack was so brutal that it would point to someone who knew her or had watched or stalked her enough to know when her fiancé worked,” said author Kathi Kresol, who has written about the case over the years.

A potential link to Peterson’s job at the Chrysler plant also emerged. It was rumored early in the investigation that she may have happened upon something unsavory at the plant and was silenced for what she knew.

“The police looked into it but never found proof of any of that,” Kresol said.

In addition to the knives and machete, a pair of bloody gloves were found at the scene. Whether the items have yielded any physical evidence such as fingerprints or DNA extracted using technology that that didn’t exist in 1979 isn’t known.

The case remains unsolved.

Anyone with information about the the death of Rosemary Peterson is asked to call the Winnebago County Sheriff’s Police Detective Bureau at 815 319-6400 or Rockford Area Crime Stoppers at 815 963-7867.