I thought the game saves after I stun the guy. But when I fell off the platform and the checkpoint loaded he was up again and a box suddenly exploded in my face. Which caused the checkpoint to load. Which resulted in a box suddenly exploding in my face. Which caused the checkpoint to load. Which resulted in a box suddenly exploding in my face.

I don't know how the checkpoint saved like that when I had survived the 1st time but it created an infinite loop forcing me to restart the level.