PORT SHELDON TOWNSHIP, Mich. -- The family of Deborah Lynn Polinsky alongside the Ottawa County Sheriff's Office are asking for tips from the public after the cold case team made a new discovery investigating the 1977 homicide.

After 40 years of police work, investigators say retested DNA evidence proves another woman was at Polinsky's home when she was murdered.

A co-worker found Polinsky stabbed to death on July 26, 1977, after she did not show up for work the day before, second-shift at Depree Chemical Company. Police believe Polinsky was sexually assaulted before she was murdered, found naked on her bed at her rented farmhouse on New Holland Street near 152nd Avenue.

Polinsky's younger sister Tami Elzinga tells FOX 17 she and her family now have some hope Polinsky will get justice. She held a photo of her sister Thursday: Polinsky was photographed at 19-years-old with family at her last Christmas.

"This kind of shows that she was a daughter, she was a sister, she was an aunt," said Elzinga looking at the photo.

Elzinga says Polinsky dropped out of Holland High School when she was 16 to go out on her own. At 20, in 1977, she says Polinsky lived at the farmhouse with her beloved pets, including a cat, a duck named Dudley, and her German Shepherd named Thor.

"She was fiercely independent," said Elzinga. "She liked to do it her way and she was very strong-willed and loved animals. She loved her pets.”

Now investigators are looking to identify the woman they believe was at the home when Polinsky was killed. No other information about the woman was released.

“That may spur somebody's memory to come forth with some additional information," said Captain Mark Bennett with the Ottawa County Sheriff's Office. "That's really all we need, that key piece of the puzzle to put this thing together and to move forward with the case.”

Bennett tells FOX 17 there is no known motive for Polinsky's death. The sheriff office's cold case team has been investigating the murder the last 40 years, with two detectives working the case full-time the last 18 months. In that time, Bennett says they've interviewed more than 180 people, sent 40 DNA samples to the lab for comparison, and analyzed more than 600 latent prints.

Polinsky was known to frequent Holland and Saugatuck and attended Holland Public Schools, he said. She was frequently seen in a red VW Beetle and was often around her German shepherd Thor.

With this new discovery, asking for any new information, Elzinga says their family has hope this case will be solved.

“I think now we have some hope," said Elzinga.

"There’s been quite a few years where there’s been no hope. More than anything, I think all of us realize we have some hope now. There’s new leads coming out and they are working strongly on the case. So that’s a big thing."

Anyone with information on this case is asked to call investigators at 616-738-4022 or Silent Observer at 1-877-88-SILENT (745368). Police say no information is too small to call in. Tips can also be submitted online.