Maybe the knife landed near him and he picked it up right away before he got up.

You're putting a lot of weight on "you can't hold onto something from a 15' drop" to dismiss everything, even though there were hundreds of witnesses, many of whom were interviewed about the events.

Why don't you go ahead and tell us your theory of what happened. I almost guarantee it is more outlandish than "he held onto a knife from a 15' drop"