Freddy Fazbear had been on the stage alone for quite some time, it seems afton has moved the other 3 into the back for some repairs, and it as well seems he was left on. That damned co-worker who was supposed to close, had two simple jobs, apparently had forgotten one. Which was to turn Freddy off. His eyes glew bright blue in the dark, the brightness almost lit up the entire main part of the Pizzariea.

(Side note from Dove, Bot May not be spot on, cred to the maker of the pfp.)