Nearly three decades after the horrific Christmas Day murder of 6-year-old pageant princess JonBenét Ramsey, dedicated investigators have identified her killers and are gathering critical DNA evidence that they believe will lead to an arrest.

The National Enquirer can reveal that the names of dozens of suspects are detailed in a spreadsheet compiled by late homicide detective Lou Smit, who before his 2010 death was hired by JonBenét’s father, John Ramsey, to investigate the case.

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Armed with the spreadsheet, which contains approximately 600 critical line items — including suspect names and important evidence details — Smit’s daughter, Cindy Marra, is heading the team of sleuths, who are relentlessly tracking down leads and chasing DNA.

“They should restart the investigation from scratch using Lou’s list of suspects,” a source familiar with the spreadsheet tells the Enquirer.

“They had the name of the person of interest during the first week of the investigation, so that alone says the suspect is on Lou Smit’s list because he had access to the police files.”

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Marra told Denver 7 News, “We decided the best thing we could do is work off the spreadsheet he developed.

“We have been able to eliminate from our list probably 25 people based on DNA.”

The explosive new breakthrough reignites one of America’s most haunting murder mysteries that made international headlines after JonBenét’s strangled, beaten and abused body was discovered on Dec. 26, 1996, in the basement of her family’s home in Boulder, Colorado.

John and his wife, Patsy, who died of cancer in 2006, were initially considered suspects but were eventually cleared. But critics have long accused blundering lawmen of allowing the true culprits to get away with the brutal crime.

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Smit, a seasoned Colorado Springs homicide detective, began compiling the vital information after being pulled out of retirement by JonBenét’s frustrated dad, who insisted she was attacked by intruders who left behind DNA evidence on the child’s underwear and underneath her fingernails — and that the DNA didn’t match any of the Ramsey family.

Before his passing, Smit implored anyone who visited him, “Please don’t let this die,” and revealed to his daughter and others a list of approximately a half-dozen “priority one” suspects, the insider exclusively tells the Enquirer.

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In December, the Enquirer revealed that one of Smit’s suspects was David Cooper, the alias of a man who contacted Ramsey 20 years ago and claimed to be a professional killer hired by one of his disgruntled ex-employees.

Cooper first contacted Ramsey by telephone, providing chilling details about his family home that had never been made public. Despite the compelling details, Boulder police shockingly asked the grieving father to do their jobs for them — even suggesting he bring the creep to the stationhouse for questioning.

“The police had no interest in looking at him,” Ramsey, 81, told the Enquirer in December.

After the Enquirer’s exposé, Ramsey and a DNA expert met with new Boulder Police Chief Stephen Redfearn to discuss running existing forensic evidence through a commercial genetic lab to see if the killers’ relatives can be identified.

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“It was a good meeting,” Ramsey told Denver 7 News about his two-hour showdown with the chief in January. “I was impressed. They were not arrogant, cocky, big egos. They were eager to talk and get the case solved.”

Ramsey, however, admitted to the outlet that the police didn’t openly “talk about everything they’re doing.”

Investigators have received more than 21,000 tips, analyzed hundreds of DNA samples and traveled to 19 states to question more than 1,000 people.

Still, they remained tight-lipped about the case when contacted by the Enquirer, refusing to say if they’ve identified a person of interest.

“Because this is an open and ongoing investigation, the Boulder Police Department is unable to give any interviews or comment on specific aspects of this crime,” Public Information Officer Dionne Waugh told the Enquirer via email.