Speculation:
1. You're right [military HALO] and they were not supposed to be seen by anyone. Why?
2. It's leftist wackos...most aren't that skilled.
3. Terrorists trying to infiltrate hard zone from the building. Alarms? Lots of two way locks getting out!?
4. False report.
My guess...four is most likely. But then again I like to play craps, not slots, which makes me a conservative gambler.
Someone just thought they saw it.(grin)