[raccoonradio]

poss. that the beacon transmitter may have failed. there was concern that if a plane were hijacked, the hijacker would have found a way to disable the beacon so they couldn't be detected (again, security erred on side of
caution) (fox n again)

Now people are seen flowing back in to the direction of the Capitol.

[mhking]

CNN: Capitol Hill police preventing people from returning to the Capitol building for about fifteen minutes or so.

[El Gato]

poss. that the beacon transmitter may have failed. there was concern that if a plane were hijacked, the hijacker would have found a way to disable the beacon so they couldn't be detected

Pretty much the first thing the 911 hijackers did after taking control of the aircraft was to turn off the transponder (beacon). They already knew the way to do that, it's just a switch after all.