Well, they just arrested 20 folks at Boston's Logan Airport (where this flight originated) with forged identities that had " access to all areas of the airport, including terminals, baggage areas, screened passenger checkpoints and runways."
I'd say that with the "secure" folks being that badly screened (if at all) it might not be too hard to have the cleaning/food services guy put a gun or bomb in the seat cushion/toilet/magazine rack/whatever.
Or maybe a gun was planted in the terrorist's bag far away from the plane by a mere baggage handler or a team of security screener(s) inside the airport!!!
to clarify before I'm crucified...I meant a security team searching carry-on bags,etc....I know it'd be hard to "draw" from the cargo hold!