Sig's Theory (Here's what happened...)
This terrible crime was a burglary gone awry.
There are two perps: one male, one female, both young adults.
One of the perps is acquainted with the Ramseys, probably through her parents. She had heard that the Ramseys were leaving for holiday in Michigan over the Christmas break.
The female perp has a male friend, a latent sociopath and pedophile. For quite some time, this toxic upper middle class couple have been burglarizing homes in the area for fun and drug money.
It is Christmas Night, and the female perp is on the phone with the male perp. She sees the Ramsey's car pulling out of the driveway and mistakenly believes they are headed for the airport. They are, in fact, merely on their way to visit friends just a few blocks away. She tells the male perp to hurry on over so they can burgle the Ramsey home together.
However, by the time the male perp gets there and they break into the residence, the Ramseys have returned home from their Christmas visit. Indeed, the perps have barely made it through the living room when the realize that the Ramseys are about to walk through the front door. They quickly hide in the basement where they wait for the family to go to sleep. They are down there for a few hours. They try to escape through the grated egress but mistakenly believe it to be barred shut. Once they think the coast is clear, they ascend the basement stairs to make their way out. However, as they proceed through the kitchen they encounter JonBenet who has just bounded down the stairs from her second floor bedroom, perhaps to have a snack of pineapple, perhaps believing she had just heard Santa stirring about downstairs. Jonbenet recognizes the female perp who she knows by name. The perps quickly whisk her down the basement, perhaps knocking her out with a stun gun.
Down in the basement, the male perp starts talking about murdering the child in order to shut her up. Perhaps he has a lengthy criminal record and fears his next conviction will get him an extended prison sentence. Perhaps he is the darling son of a politician, judge, or law enforcement officer and cannot bear the shame of getting arrested. Whatever the reason, the male perp is dead set on not going to prison, and the crystal meth he's on is making him all the more psychotic. The female perp, who knows the child and is not nearly as sociopathic as her accomplice, tries to persuade him to kidnap the child instead. She goes upstairs where she finds pad and pen and sets to writing a ransom note, stealing lines from crime movies in a flimsy attempt to sound like a believable kidnapper and political radical. Unfortunately, by the time the female finishes the two and a half page note and returns to the basement, her sociopathic accomplice has already brutally murdered the child. She screams upon seeing the body. The scream is heard by neighbors as it bellows out the window of the grated egress. However, it is not heard by John and Patsy Ramsey who are fast asleep on the the third floor. The perps eventually make their way out of the residence, leaving the body of Jon Benet in the basement.
End of story.