I think Glitchtrap controled him

No he did not

Woah nah. Don't tell me you've been binging those garbage gacha life videos to think that

Glitchtrap and william are the same people so that wouldn’t work

Yeah it's digital

The kids epically trolled him on Xbox live one too many times. This made him so mad he decided he'd troll them back by precisely planning out how he was gonna murder them at their favorite pizzeria.

The true lore revealed

William is just insane because his favourite child died (elizabeth btw)

@SuperSajanBonnie But Charlotte Emily died first then Fredbear killed Crying Child/Evan/ then William murdered 5 children and after 5 missining children Elizabeth is killed by Circus Baby.

There is not a definite answer. The reason why he did it is up to debate.