Another wacky thing to do for that level - at the beginning, all the tourists start walking toward the door, but one woman breaks off from the group, goes behind the bus, puts down her suitcase, and walks a few yards away to have a smoke. Make sure you start with a sniper rifle, then swap your rifle case with hers and she'll pick it up a few seconds later.
She gets owned by security and you can waltz in and grab the case
That level took me a MILLION tries.
So did the last one, come to think of it. Let me know if you want a tip for that one as well.