In regards to Linda Arndt's opinion on who committed incest against JonBenet and the family dynamics involved, here's a link to a deposition she gave. It's worth reading in its entirety but the incest part starts on page 42 of the document (use your browser's word search function, searching for the word "incest"):
http://www.acandyrose.com/03182000-arndtdepo-04102000.htm
1 John Ramsey and JonBenet and no other family members?
2 A. I refer to every member of the family.
3 Every member has got a role.
4 Q. But in terms of an actual sexual act that's
5 implicit in the term of incest, you're referring to
6 John Ramsey and JonBenet?