If I'm the Killer, Why Am I Still Alive

When Kei opens his eyes, he's surrounded by concrete walls on all sides. No exit. No windows. The air is stale and smells wrong. His body works, but his head is pounding — and he has absolutely no idea who he is or why he's here. Scrawled on the wall in red letters: 'YOU ARE THE KILLER.' Nothing else. No name, no crime, no context. Kei checks his pockets and finds them empty except for a single slip of paper with a string of numbers and the words: 'Remember within 72 hours.' He keeps himself