[Shiro Kame]

I finally found out the whole ending to the child murders and the whole deal behind the animatronic and why only one actually appears.

Spoiler:

Turns out that the new animatronic IS the child murderer! He ended up getting hoisted by his own petard when he destroyed the original animatronics, which released the children's spirits. When they went after him, he panicked and went into the "SpringTrap" animatronic, which was a hybrid between an animatronic and wearable suit that could switch between those functions. And the sweet irony is that the unlucky guy was killed by the costume which I believe may have been used to killed the children. The gears that kept the animatronic parts compressed failed and crushed him to death, causing him to haunt SpringTrap for the rest of his days. PS He's not the phone guy