Justice for late beauty queen JonBenét Ramsey took a step backward when a key murder witness died last month, adding to the number of people intricately embroiled in the still unsolved mystery who have perished.

Melody Ann Stanton, a Boulder, Colorado, neighbor who heard JonBenét’s bloodcurdling scream in the wee hours of Christmas 1996, died April 12 at age 77.

“The principals of this case are dying — and others are forgetting what happened because of old age,” says an expert JonBenét investigator. “The case is getting colder, and authorities are not willing to do the work to solve it.”

Stanton emerged as a vital witness shortly after the strangled, sexually abused 6-year-old girl was found in the basement of her family’s Boulder mansion.

“I heard a terrible sound,” Stanton recalled in 1997. “It was the longest, most horrible scream I have heard in my entire life. It sent shivers down my spine. I could tell the sound was coming from the Ramsey house, and I knew instantly it had to be their little girl.”

Stanton told detectives she’d gone to bed about 10 p.m. with her window cracked open and was awakened between midnight and 2 a.m. by “one loud, incredible scream.”

She added the cry was “obviously from a child” and lasted three to five seconds. After that, she said she did not hear additional cries or a vehicle peeling away from the scene.

Stanton joins a growing list of witnesses, investigators and persons of interest who have died since JonBenét was snatched from her bed, sexually abused, bludgeoned and garroted. They include her mom, Patsy Ramsey, who died of ovarian cancer in 2006; retired detective Lou Smit, who was hired by JonBenét’s father, John Ramsey, to investigate the case and died in 2010; and Bill McReynolds, aka “Santa Claus Bill,” a close family friend and person of interest who died in 2002.

In a desperate bid to solve the case, JonBenét’s 80-year-old father recently petitioned Colorado Gov. Jared Polis to move the case from the Boulder Police Department’s control and allow the state police and an independent genealogy firm to test the DNA evidence found at the crime scene.

“We think there’s still hope for some movement and progress based on the new leadership in the organization,” says Ramsey. “So, we’re cautiously hopeful that there is some progress and effort being made to do those things we’ve asked be done.”

Police have received more than 21,000 tips and traveled to 19 states to question more than 1,000 people. They’ve also analyzed hundreds of DNA samples in the lingering case. But despite some renewed efforts, time is not on the side of justice.

“We’ve had this narrowing window of opportunity, and we really are at a critical juncture,” warns JonBenét’s half-brother John Andrew Ramsey, who was 23 years old when his little sister was murdered. “We got the right DNA tech, we got witnesses, and people that have been involved in the case are still alive — likely the killer as well. And now we’ve got this new push from the police to find the killer. It’s a great opportunity, but it’s not going to last forever. People are already dying off, and that will include the killer at some point.”

He insists more can be done by the police. “We can’t be overreliant on DNA tech,” he explains. “At the end of the day it’s going to take investigators who just have a dogged pursuit for the truth. Of course it’s too late. This should’ve happened 26 years ago, but here we are.”