Because that's the last thing you'd expect them to doIf the FBI (or any other 'inside' agent) wanted to plant bombs (in the twin towers, at the finish line to the Boston Marathon, wherever) why on earth would they want MORE security? Just explain, in your own words, without a youtube video, why their actions could possibly be assisted by having (presumably out-of-the-loop) security EVERYWHERE?
Well quite. If they wanted to blow the place up, what the hell do they need sniffer dogs for? Why involve more and more security that need to be part of the cover up. Just set off some bombs, job done.Far more likely, if there were bomb squads and security everywhere, is that they'd had intelligence that a group was planning an attack but weren't able to shut it down in advance. IF that's the case then there's a question as to whether they should have proceeded with the event (of course we can never really judge that without access to the evidence that the security services had) but that's the worst accusation that could be levelled at them.