After thinking about it for a while I would say NO, he wasn't involved! It all seems too implausible for me to believe he accidentally killed her and then the parents covering up for him. We would have to believe too many crazy things IMO for the family theory to be true. These piece of evidence that Lou Smit brought up are enough for me to trust the intruder theory -
The intruder left no footprints because he went around and avoided the snow -
http://i.imgur.com/AzYkumz.png /
http://i.imgur.com/7lThNRs.png /
http://i.imgur.com/9Azf8FG.png
Foliage trapped underneath the metal grill, which the intruder moved to get inside the basement -
http://i.imgur.com/TWtMJep.png
And we see a disturbance when he landed his feet underneath the metal grill - http://i.imgur.com/1aRmDJs.png
The intruder left his fingerprints on the window he used to get inside the basement - http://i.imgur.com/3YmHVpI.png
The intruder left a shoe print on the briefcase he used to escape the house - http://i.imgur.com/UCummhi.png
Left a shoe/sneaker mark on the wall and left the window open - http://i.imgur.com/KowhrYl.png
(WARNING: GRAPHIC) JonBenét's stun gun marks - http://i.imgur.com/U82Ck5H.png
With the electric arch clearly seen here - http://i.imgur.com/E8lQ2E6.png /
http://i.imgur.com/YVyNHuW.png
The garrote used to strangle JonBenét was pulled so hard and violently that pieces of her hair were stuck on it, you really think her parents or brother could have done that? - http://i.imgur.com/2Nyxga2.png /
http://i.imgur.com/NdwTliI.png
(WARNING: GRAPHIC) JonBenét was strangled so violently you can see red marks around her entire neck - http://i.imgur.com/BuwGhBz.png
(WARNING: GRAPHIC) So it wasn't just "planted" their by her parents to make it look like a strangulation. She really was severely strangled -
http://i.imgur.com/solzTQ3.png
(WARNING: GRAPHIC) Her fingernail marks on her neck suggesting she was fighting back against the strangulation proving she was alive first & strangled. Then she was hit over the head that cracked her skull and died shortly after the blow - http://i.imgur.com/P7ydZLV.png
To me this makes more sense then the "family did it" theory. I can't see Burke hitting her so hard to crack her skull then the parents finding out and covering it up by strangling the daughter they loved very much in the basement to cause severe marks around JonBenét's neck, then sexually assaulting her, then breaking the glass window in the basement, leaving footprint marks, writing a note under great emotional stress and saying they would "behead" their own daughter? The language in the note suggests an intruder wrote it because the language used in the note would not come from an intelligent and caring person like Patsy who loved her daughter too much. Patsy or John didn't have that kind of vocabulary, sorry I just don't buy it. Leaving her dead and cold in the basement like that and pretending not to know where she is when the cops came, that's crazy.
Even the phone call makes sense when you accept the intruder theory. Patsy saying "what did you do?" "Help me Jesus" implies her not knowing anything! Why would she say that off the record when she knew nobody was listening to her, if she knew her daughter was dead in the basement she wouldn't have uttered those words. When they woke up in the morning they may have taught Burke did something to her that's why even John said "we're not speaking to you" but Burke was innocent, it was just a false assumption by them. No, these parents would have died for their children, they loved them too much, they had too much invested in them! You can just tell.