"Around 2001, John Karr and his family moved to California. Around that same time, Karr also began doing research for a book he wanted to write about men who commit crimes against girls, Nate Karr said. He believes the research, which included reviewing police and coroner reports about the JonBenet murder, may have been what landed his brother in trouble"
This may be why Karr knew so much about the murder.
The guy said he drugged her. But the autopsy report says no drugs found:
http://www.thesmokinggun.com/archive/jonbenet1.html
Not trying to vilianize the parents, at all, but I will never understand these parents that let men spend time with their children. No strange man is ever or will be ever around my kids without me in the room. Ever. There is no valid reason a grown man wants to or needs to spend one on one time alone with a child.