Imo, I think it could quite possibly be pilot error given the weather conditions, but the only question I have is: "Why is the pilot so stubborn?"
You've got a plane-load of VeryVeryVIPs, and try landing at the same airport 5 times without switch airports with considerably better facilities?
Unclipped video:
http://www.youtube.com/watch?v=q7yD_SVK7Yw
Aerial Picture of crash site:
http://bi.gazeta.pl/im/3/7765/m7765863.jpg
From the aerial picture, seems quite probable that someone can catch it on film. Keep in mind that a presidential aircraft would look like any other aircraft to someone that is unfamiliar.
(Oh, and the gunshots could be the emergency oxygen tanks exploding.)