How did he get on the active runway...?
Not that there is a physical barrier or anything...but it makes you wonder if he attempted to get a TO clearance...or if there was any conflict with other arriving or departing aircraft. Who knows if he even took off in the right direction...

In hindsight it would have made a lot of sense to evacuate the terminals, and Sea-Tac tower. Also, tall structures like the Space Needle...

I can't imagine the mood in the SEA tower knowing you are a possible strike candidate for the end of that bizarre drama.