Hogart is.
1664
Lynch or Radcircles
But, during the season finale, all the clues point to Cameron. So, I don't think it is clear on who RadCircles is, because it can still be anyone. :) Hope this helped
Radcircles is Lynch. The episode aired today. Lee goes into Lynches house and sees the voice synthesiser, a picture of his shadow and a lot of KNOCK KNOCK posters stuck to the walls
It is revealed in Detentionaire that Barrage, the school's head of security, framed Lee Ping for a prank he didn't commit. Later in the series, it is discovered that Barrage was manipulated into doing this by a secret group known as The Council.