Of course, it all makes sense now!

Dirty Harry did it!
He was the guy on the grassy knoll!
The "magic bullet" was really from the .458 Magnum he used in the first movie!
What became of that gun?
Why was Clint was hiding out in Italy making spaghetti westerns in mid 60s???
Why did he make "Line of Fire", where he plays a Secret Service agent who had been on JFKs detail when he was assassinated?

It all adds up!

I bet if I play all his movies backwards, I'll find a hidden message!

Hope I didn't just spawn a new conspiracy theory. But it makes as much sense as a lot of the ones floating around:-)