HijackersScreened

From 911Encyclopedia:

As Policetalk.com reported in March 2002, nine of the 19 hijackers were searched before boarding, as claimed in this article: "Nine of the 19 terrorists who hijacked four jetliners on Sept. 11 had been singled out for special scrutiny that morning under aviation-security guidelines, government officials said today, as they looked back sadly at what might have been. But because their baggage contained no explosives, the hijackers were allowed to board." http://www.policetalk.com/9_hijackers.html

The unanswered questions are: Why is there no airport security footage of them? How did they (allegedly) get on board with knives, guns, AND electronic guidance systems, while being searched, but avoiding security cameras and not being on the passenger lists? What aliases were they alleged to be using when they were searched, and if they were not using aliases, why are they not on the passenger lists?