In a panic, you grab for your sidearm and open fire, shooting wildly at the security guard.
One bullet hits its mark in the man's throat. He falls backwards and collapses to the ground writhing in agony, gargling and choking as blood fills his wind pipe, until finally he seizes up, his eyes dead and lifeless...
You have to hurry. No doubt someone heard the gunshot. It was quite loud. You should probably leave immediately, but you can see he had some nice body armor. That could be useful.