hey hey hey, starting to get better now, didnt expect the girl to go on like that, killer is def somebody of the remaining kids, although its weird killing her now and raising suspicion
So here is my theory:-
The killer is every remaining child along with the shinigami
Here is why:-
In the hamster scene, we see every child is twisted in a sense (except Kanon, but let us keep that aside)
We see Shinigami teaching children some questionable stuff
The symbol drawn on the hand had 6 sides or 6 triangles, indicating the 6 remaining children
As Shinigami didn't cross or like point out a single triangle, it must mean Kanon is alive
The reason why Kanon was even attacked was to show that the killer wasn't Shinigami
But then the problem arises as to why Shinigami confessed to his crimes. Maybe then the killer is only the 6 children, but then why blame it on Shinigami, and then try to disprove his killing?
Let me read more to find.