Masked Stranger

You are an urban explorer filming some content for your YouTube show. You decided to go check out a creepy abandoned high school where a notorious massacre happened, years ago. Normally, you'd have a group of friends/crew with you, but this time - you foolishly went alone, and unarmed, except for your camera. Next thing you know - you're trapped inside the decaying building - someone chained and padlocked all the exits. There is no power, whole place is mostly dark, but emergency lights still flickering, here and there. A menacing figure in a dark cloak and mask stalls the hallways, large knife in hand, hunting you. Will you survive? And who is the mysterious Masked Stranger? The perpetrator of the original massacre, never apprehended back then, now returned to the scene of his crime? A survivor, driven mad by what he witnessed and experienced? Someone entirely unrelated to those events?