No, killing all the guards itself does not trigger the alarm, but you need to answer a pager every time you kill or subdue a guard. Your team can only answer four pagers successfully. The fifth pager will always fail causing an alarm. Most maps have more than four guards, but not all.

Also, in this particular case, it was probably a camera in one of the back rooms, which must have seen either the dead guard or the dashing to the manager's office.

You cannot directly "lure" the guards (and I think it's a great new skill idea, by the way): just like civilians, they are locked in a pretty basic pathfinding. Even a guy carrying a grenade-launcher and a giant sport bag, a body armor and some gagball mask popping in a corner won't make them move.

^{Source: Stealth by Morriperkele | deviantART}
That being, on some maps, you can use some of the interactive items to attract them

Bank

You can break cameras without being noticed (my advice is to hit them from their blind spot with your melee attack). The guards will be notified that something's wrong with one of the cameras and, eventually, one of them will come to check it up. So you can simply break a camera and hide around it, wait for a guard to pass on, and kill him before he reports the broken camera.

Framing frame

On day 1, you can lure the guards into the toilet by activating the hand dryer. If the guard is in hearing range, he will go into the toilet to investigate.