Before I start, I have to say: I apologize for getting the culprit wrong last time, this time i'll give who definitively did the bite of '87. I let my Withered Freddy bias get through and that wont happen again. Anyways, the withereds can't be the culprit since this happened during the day and they shouldn't be roaming around, The Puppet and Balloon Boy are disqualified due to them not even having movable mouths. Toy Freddy and Toy Bonnie's mouths are too small to even do significant damage, Toy Chica doesn't even fucking have a JAW. So that leaves one suspect left, the one who truly did the bite of 87:

ENDO-02 IT WAS HIM ALL ALONG HE DID IT HE DID IT AAAAAAAAAAAAAAAAAAAAAAAAAAAA IT WAS HIDDEN IN PLAIN SIGHT GRAAAAAAH

Nah I'm just kidding, the real culprit, after years of speculation, turns out to be....

Funtime Foxy, the Mangle.