I have, what some would call a morbid interest in true crime, when I was about 14 I asked for a book for Christmas 'The Cases That Haunt Us', it is by an FBI profiler, John Douglas, who started profiling/behavioral science (in criminal investigations) back in the 1980's, the character from Silence Of The Lambs, the FBI agent, was based on him. So, I read it on Christmas Day, and I vividly remember the Jon Benet chapter,(have read many times since, well worn book on the shelf) the grotesque sense of irony not lost on the 14 year old me, as I read about her brutal murder and sexual assault....The book covers Jack The Ripper, Lizzie Borden, Zodiac, and what it does is from the behavioral clues, left by the suspect, analyzes who the killer likely is/was.....Douglas, wrote on the OJ Simpson murders too, but thats a different thread/topic.....Anyone interested enough, I'd say buy the book, and you will have your answer, the short version is that the parents were not guilty of anything, nor was the brother. You have to really delve into the ugliness and brutality of the crime, as well as the analysis of that brutality.....This is one of those cases that got mishandled by the investigators, and the media coverage, but a little background on behavioral profiling and the crime, and it's clear what happened....that doesn't mean we will ever know who it was, but you will know who it wasn't. That ransom note is a pretty important piece of evidence, in itself. Tells you a little about the offender...the most important thing is look at what actually happened to Jon Benet, awful as it is, and then go from there.
*Also, in MANY, possibly most, of domestic murders, of children, the parents or someone close to the family, are often the guilty party, this is not the case here.
When you use those profiling procedures, and behavioral science techniques, almost every crime is solvable to a degree.
And whatever you do, don't fall into CIA theories, or satanic rituals, or whatever bullshyt link that is....wow that is just frustratingly stupid.