I'm more inclined to think he's a high schooler who should be in school and isn't. This is too immature to be done by someone with an actual agenda.
The time of day that these generally happen would lend credence to your thought -- perhaps a kid who posts his hit & run just before hopping the bus to school. In that event, his parents/parole officers would probably be very interested in this.
Also, as I said before, I'm sure this violates his ISPs Terms of Service.
If he can be tracked, I'm sure we can get his internet access revoked if nothing else.
Whatever the agenda, the pictures were more than just offensive. They leave quite an indelible image.