Do you believe Dougherty used the West elevator immediately before and after the shots?
The problem is that Dougherty claimed to be right beside the north stairwell. If his memory is correct, he should have seen Oswald (or whoever fired the shots from the 6th floor) coming down the north stairwell.
If Oliver Stones JFK movie is to believed, a whole group of assassins were on the 6th floor at the time. Dougherty needs to explain why he heard no one come down the stairs.
Seems odd. Dougherty heard no one come down the stairs and neither did Adams and Styles. Maybe the stairs weren't as noisy as people claim.