My final prediction: Lucas is AD and why he is AD extends all the way back to earlier seasons as well

Marlene has said that they intentionally put AD clues in these final 10 episodes so we will know who it is, but she also said the reveal of why AD is AD will be the most interesting. So, the way I take it, is that the reveal of who AD won't be as important as compared to why he/she did it.

I've always suspected of being AD for a long time. Even in earlier seasons I thought he always had an agenda for the teasing that Allison had put him through long ago