During the development of the Five Nights at Freddy's story, there was a theory suggesting that Mike Schmidt, the protagonist of FNaF 1, was originally conceived as the true killer behind the franchise's macabre events. This idea is based on various clues left throughout the games, which, when analyzed, suggest a more direct connection between the character and the horrific crimes that occurred in the pizzeria.

Scott Cawthon mentioned in interviews that, during the production of the first game, many fans, especially after watching the Game Theory video on the subject, had uncovered much of the story. In that video, the theory that Mike Schmidt was the killer gained prominence, being seen as an "obvious" interpretation by many.

In the first game, the enigmatic phrase "It's Me" appears repeatedly. Traditionally, fans have associated this message with Golden Freddy, but if we consider the theory that Mike Schmidt is the killer, this phrase takes on a whole new meaning: "It's me. I am the killer." This interpretation suggests that Mike is confronting his own guilt or perhaps being haunted by his past actions. This is reinforced by the hallucination where we see Freddy's eyes, with the blue pupils possibly indicating that it is Mike, perhaps wearing the animatronic suit.

There is also the idea that Mike Schmidt was not just a new employee at the pizzeria. Instead, he was a former employee who had used his position to lure children to the back rooms, where he killed them. At the time, these back rooms would have been the Backstage, areas restricted to authorized personnel. Mike might have returned as a security guard to revisit the scene of his crimes, possibly being tormented by his actions or wanting to reconnect in some way with the victims he himself created.

This narrative creates a dark and disturbing plot for FNaF 1: throughout the game, the animatronics are portrayed as the villains, but the final revelation would be that the real monster was the player themselves, personified by Mike Schmidt. He was the maniac who killed the children, and the animatronics, seen as threats during the game, were actually the haunted victims seeking justice.

This theory also extends to FNaF 2. The Phone Guy's lines, such as "Especially concerning any... former employees," could be referencing Mike. At the time, it seemed that Scott planned for Mike Schmidt and the infamous Purple Guy to be the same person, with the latter depicted as a security guard, just like Mike.

The Purple Guy's security badge reinforces this connection, suggesting that Mike was the "former guard" mentioned. Additionally, the cryptic image of a skull with the name "Mike" could be a hidden clue placed by Scott in the game files, indicating this relationship.

Over time, Scott Cawthon further developed the story and characters, revealing that Mike Schmidt and the Purple Guy are, in fact, Michael Afton and William Afton, respectively, father and son.

EDIT: I'm not saying Mike is the killer; I'm saying that Mike was planned to be the killer at the time.