Holy Cow! I was on the flight! I have a posting regarding how I wound up w/ a MX CX the day before:
http://www.flyertalk.com/forum/showthread.php?t=815704
When we were about 20 minutes before landing, the Captain came on the PA and said there was an "issue" and authorities were to meet us at the gate. As a result, everyone must stay in their seats until the Captain allowed us to get up (even after parking at the gate).
We literally sat there for 5 extra minutes with our belts buckled; there were at 2 fire trucks outside and a paramedic vehicle as well. Wasn't sure what was going on. They also announced they were looking for witnesses to the incident.
Dang, now I really wished I got up to walk around during the flight; I chose to just sit in my seat the whole flight... I guess I missed the show!
I noticed at least 2 or 3 additional UA staff (and I mean people in suits) hanging out by the F/C exit with United envelopes. I wonder if they were Skykits or some kind of comp.