Were They Trick-or-Treating as Squeaky Fromme?

Yesterday, reports the AP, a couple of House staffers brought Halloween costumes to work that apparently featured a toy gun.

How did the Barney Fifes running the security op at the Capitol respond? As Marvel Comics auteur Stan Lee used to say, read on Macduff:

Start to finish, the incident lasted two hours or less ? but it triggered a massive security response in a time of terrorism worries. Police in battle gear moved into the House's Cannon office building in pursuit of suspects. Across the street, the House was placed into an unscheduled recess for the first time since the aftermath of Sept. 11, 2001.

[U.S. Capitol Police Chief Terence] Gainer said the staff aides had stopped to chat with security personnel after placing a bag on a security station X-ray belt at the entrance to the office building, then went into their building. Moments later, security officials noticed the image of a gun on a video screen, and triggered an alarm.

Beyond underscoring the lameness of Capitol Hill security, the accounts I've read fail to answer the most important question raised by the story: What the hell was the costume?