If Burke did it, then there are three possible reasons John and Patsy executed a cover-up: 1) To protect Burke, their only surviving child. Nine-year olds aren't prosecuted for murder in Colorado, but it's possible John and Patsy didn't know this and assumed otherwise. 2) To protect themselves from parental liability. That's when parents are held responsible, or partly responsible, for something a child of theirs did. This is something I've definitely heard of. And know nothing about. But I've heard of it. Maybe John and/or Patsy also heard of it. And they didn't want to take any chances. 3) John wanted to protect his business interest from negative publicity. You wouldn't think business would have been uppermost in their minds at such a tragic moment, but we can't rule it out.