NEW: Terrifying surveillance video shows employees scrambling for cover inside an In-N-Out Burger as a gunman opens fire at the drive-thru in Twin Falls, Idaho.

NEW: Terrifying surveillance video shows employees scrambling for cover inside an In-N-Out Burger as a gunman opens fire at the drive-thru in Twin Falls, Idaho. As workers try to protect one another and escape, an off-duty Idaho State Police trooper inside the restaurant draws his weapon and runs t…