The mystery of JonBenét Ramsey's killing in 1996 is a puzzle whose missing pieces seem only to grow in number, frustrating professional and amateur sleuths
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Almost 20 years after the 1996 murder of 6-year-old JonBenét Ramsey in Boulder, Colorado – her killer is still free. Subscribe now for an inside look into the case that continues to haunt the nation, only in PEOPLE.

The mystery of JonBenét Ramsey‘s killing nearly 20 years ago is a puzzle whose missing pieces seem only to grow in number, frustrating professional and amateur sleuths alike.

With a fresh review of the investigation in this week’s issue, PEOPLE looks at the enduring questions, whose answers could point to the killer of the 6-year-old pageant contestant found beaten and strangled in the basement of her family’s Boulder, Colorado, home on Dec. 26, 1996.

Five of the most pressing:

1. Was There Really an Intruder?

Investigator Lou Smit tallied a broken basement window, an unidentified footprint near the body and trace male DNA evidence on the scene, and went to his grave in 2010 believing the answer to that question was yes.

But Boulder police considered those signs inconclusive. They pointed to dust and an undisturbed spider web around the window as evidence that undermined the intruder theory.

2. Did Someone in the Ramsey Family Write the Ransom Note?

Before JonBenét s body was discovered, her mother, Patsy Ramsey, placed a frantic 911 call to say her daughter was missing and a note had been found.

Again, there were tantalizing clues: The note was written on a pad found inside the home with a black Sharpie that also belonged to the Ramseys, and it demanded $118,000 – the exact amount JonBenét’s dad, John Ramsey, had recently received as a bonus.

Yet fingerprints on the page – revealed to come from the authorities who handled the document, as well as Patsy – never definitively identified the author.

To read more about the latest in the JonBenét investigation, pick up this week’s issue of PEOPLE on newsstands Friday.

3. Were John and Patsy Fully Cleared as Suspects?

In 2008, yes: Advances in DNA testing led then-Boulder District Attorney Mary Lacy to state that based upon a review of very specific material collected from JonBenét’s body and the scene, nothing linked the parents to the crime.

But her announcement struck others as a premature dismissal. Former Boulder Police Chief Mark Beckner said in 2015: “Exonerating anyone … is absurd.”

WATCH: Story Behind the Story: JonBenét Ramsey’s Unusual Ransom Note

4. Outside of the Family, Who Have Been the Main Suspects in the Case?

Police considered a man who visited the home two days earlier and sometimes worked as Santa Claus. His own daughter had been abducted 22 years earlier, and his wife had written a play about a child molested in a basement and then murdered.

Police also looked at a reported salvage yard worker who allegedly wore boots of a type that matched a footprint in the basement, and who committed suicide in 1997.

But neither has been tied to the killing.

5. Is the Case Close to Being Solved?

Two detectives are still assigned to it, a spokesperson for Boulder’s current police chief tells PEOPLE.

John Ramsey has said he’s put his faith either in a DNA match or someone’s eventual confession. But he’s also noted the passage of time without an answer.

“The longer it goes,” he said in 2012, “the harder it gets.”

Reporting by VICKIE BANE