I worked in IT Support for my 38-year work career, having lived thru countless layoffs, I watched a good friend get escorted out of the office one day when armed security arrived, came to his desk, told him to stand up and empty his pockets of anything that belonged to the company, told him to identify any personal items on his desk, the company would box them up and mail them to his house.
Usually, when IT employees get fired or laid off, escorting them out is standard operating procedure.
That wouldn't have helped in this situation. The perp wrote software that ran when his account was disabled after he was fired.
He planned this well before his termination and had a built in trigger if his user account was even deleted. It was a time bomb.
True, but he planted the code to monitor if he still worked there, and trigger if not.