After viewing the video,Nathan has geared up on top of the building and seemed to be in a rush (this could be adrenalin), we can clearly see that in Nathan's last video shot by a close friend he is gearing up with his bridle laying on the ground, the person who was with him was not a base jumper and would not have noticed that Nathan has misrouted the bridle for static line and had it routed through his leg lateral on his rig.

Nathan had 1 year of experience and has done atleast 10-15 static lines previously but this habit of gearing up with the bridle outside of the boc has inevitably killed him.