The biggest issue is the link of Patsy to the Ransom note, the handwriting samples, the RN analysis. It's hard to say that the chemo diminished Patsy's strength and she was frail. Patsy was diagnosed on July 4th 1993. Her final chemo treatment was somewhere in the ballpark of March 1994. She had 1.5 years to recover. If the swing was done right, Patsy could have caused the injury.
The biggest JDI advocate out there is DocG.
Solving the JonBenet Ramsey Case Some people here will tell you how wrong DocG is because he vigorously defends his theory and ignores some evidence. That's true. For me, I believe DocG only went so far on the case, decided he had it and stopped asking questions. Case solved. That's it. The end.
John's motive is always sexual. He's not portrayed as a pedophile who seeks out children, but as a sexual situational aggressor. Basically, if Patsy isn't available, he'll turn to his daughter if they're in the right place and time. In this theory, John knows he'll be exposed so in a moment of panic, he kills his daughter. He's 52 at this time in his life, has money, and can seek out call girls for his sexual needs if he's so inclined so turning to his daughter makes him infinitely worse if he did such a thing.
JDI is a valid theory. It's every bit as valid as PDI. I'm not in the BDI camp not because I don't think Burke could have done it, but because James Kolar's most compelling piece of evidence, the train track, is wrong. It's like Lou Smit and the stun gun--easily debunked.