Putting students in a state of mortal dread, and hammering it home by having a disguised person pull on the doorknob, is nowhere near the same category as a fire drill.
These teachers pulled a prank that went wrong. Someone should have thought ahead that telling kids there was a gunman on the loose so soon after the VT killings was about the worse thing they could have done. I suspect that several teachers will pay for this mistake with their jobs and the tax payers will pay out a settlement to the families.