John Ramsey tells PEOPLE he wishes police in Boulder, Colo., did a better job investigating his daughter’s long-unsolved murder.

Over the years, speculation about who killed JonBenét Ramsey in 1996 has run rampant.

The list of possible suspects in one of the most sensational murder cases of all time — when the 6-year-old beauty pageant contestant was found dead in the basement of her family’s Boulder, Colo., home, on Christmas morning — is long.

The list includes everyone from her parents, John and Patsy Ramsey, to her then 9-year-old brother, Burke, to convicted pedophile, Gary Oliva, and former teacher John Mark Karr, who confessed to killing her in 2006 but was never charged in connection with her death.

But one potential suspect stands out, at least to her father: a masked intruder who snuck inside the home of a 12-year-old girl in Boulder, Colo., nine months after JonBenét’s murder. The suspect raped the girl and then ran away when the child’s mother scared him off.

“To me, it could easily have been the same person,” Ramsey tells PEOPLE in an exclusive interview.

But, John adds , “The police blew it off as, ‘No, it’s not the same.’”

John opens up to PEOPLE exclusively ahead of the upcoming Netflix docuseries Cold Case: Who Killed JonBenét Ramsey?, streaming Monday, Nov. 25.

The three-part series takes a fresh look at the murder case, which began when John found his young daughter dead in a dusty basement room in their upscale neighborhood.

John Ramsey. 

John and his late wife, Patsy, also found inside their home a threatening hand-written ransom note presumably left behind by the killer.

But the deceased girl’s parents quickly became suspects in the sexual assault and murder of their daughter, who died from strangulation and a blow to the skull.

Netflix’s three-part docuseries goes in-depth into what John considers to be missteps made by authorities when investigating JonBenét’s murder amid an international media frenzy that only made things worse.

Patsy and John Ramsey. 

He says he is speaking out in part to encourage someone to come forward with new information and to “put pressure” on police to use advances in DNA technology and genetic genealogy to finally catch JonBenet’s killer.

When talking to PEOPLE, John expressed his shock when he learned the unidentified 12-year-old girl had purportedly been raped in the middle of the night, two miles from where the Ramseys lived — and that she went to the same dance studio as JonBenét.

“I think the method of operation was exactly the same,” he tells PEOPLE. “I believe the killer was in the house when we came home, waited til we went to sleep.”

In the case of the 12-year-old girl and her family, “they came home, set the burglar alarm, and the killer was already in the house. A very similar method, and yet the police blew it off. It was the same investigator as our case,” John says.

“But even the father of the little girl said, ‘On a scale of one to 10, I rate the police minus five.’ They just … just bone-headed ignorance. But yes, I think that was very possibly the same person.”

John, Patricia and Burke were never charged in connection with JonBenét’s killing. Patsy died in 2006.

The three-part Netflix docuseries Cold Case: Who Killed JonBenét Ramsey? begins streaming Monday, Nov. 25.