40 years later, police still hope to solve Holly Branagan murder in Bethlehem, Pa.

BETHLEHEM, Pa. (WPVI) -- Holly Branagan of Bethlehem, Pa. was murdered 40 years ago next week.

Northampton County District Attorney John Morganelli says his Cold Case Unit has been working on the case since the late 1990s, but even with advanced investigative tools now available, most of the evidence collected from the crime scene is either tainted or destroyed.

Morganelli says, "Unfortunately, despite our best efforts, even retesting the evidence that we were able to retest with updated DNA, we were still unable to bring this case to a conclusion with an arrest."

It was late March 1979 when someone entered the Branagan family household.

Holly, who was the only one there at the time, was later found by family members returning home.

She was dead on the kitchen floor with a knife plunged into her back.

Over the years, investigators have received countless tips and phone calls.

They even had people referred to as persons of interest, but with the lack of solid evidence, and no witnesses, the trail remains cold.

Four decades later, people who live in this quiet neighborhood still talk about Holly.

Wendy Stickle, who lives down the street from the old Branagan family home says, "It's terrible when they don't find the person, or the family doesn't get closure. And I think that's important and it's something you don't think about or talk about. That's the biggest thing I think about."

And Morganelli, who is retiring from the DA's office later this year says he would like nothing more than to convict the person responsible.

"It would be a great way to end my career here as DA and I wish I could do it. We'll have to see what develops over the next eight months if anything," Morganelli said.

During one of his final TV interviews five ago, Richard Branagan said he lives with his daughter's death each and every day.

He died In 2016 never knowing who did it.

Anyone who might have any further information about this case is asked to call Bethlehem Police.