"In the six weeks prior to the Oct. 23 raid, Barayev's group had accumulated weapons and explosives in a nightclub located in the same building as the theater, Moscow region Governor Boris Gromov told RIA-Novosti. The nightclub Central Station has ties to Ruslan Baisarov, a businessman in the Moscow Chechen diaspora, according to the news agency. The club had been renovated and several Chechens participated in construction work. Barayev's people disguised themselves as workers and hid explosives and arms in the club's back rooms, RIA-Novosti said."
Clearly it is past time to screen construction workers.
One of the guys that was caught getting a drivers license illegally in the Memphis area supposedly had worked on the sprinkler system in the World Trade Center before the 9/11 attacks.