Facebook killer Steve Stephens was undone by McDonald's employees who ID'd him and made him wait a little extra time for his order so the cops could come and catch him.

Stephens went through the drive-thru at the McDonald's on Buffalo Road in Erie, PA when one of the workers recognized him. He ordered a 20-piece McNugget and a large fry ... but workers made it seem the fries weren't ready so they could buy time.

According to the restaurant's manager ... Stephens got his nuggets, but then said he had to go and he drove off without the fries. It was enough time for cops to get on his tail.