This boy is clearly very disturbed. He refers to himself as “a little kid who is f***ng psycho”.
He had to have had help on making the video, coming up with the text of the message (notice how he does not hesitate or repeat in the way people normally do when improvising a message), reading it or memorizing it, and then posting it on YouTube which removed it. If you read the comments, there is even more hate there.
Whether the kid can be located and helped, and the adults helping him arrested, remains to be seen.