I think A is Lucas. I must admit that I thought for some time that it was Ezra but I have since then changed my mind.
A is obviously from season one as previously mentioned from a short video from the director, so I went to IMDB to look up the cast from season 1. Lucas was listed from 2010-2016, which got me to thinking. Why? Other than the main characters, such as the girls, some of their parents and some of their boyfriends, Lucas is the only one listed to be on the show through 2016.
Since season 7 will air next year, it just stands to reason that Lucas is A, because there is really no reason to bring him back if he wasn’t. He was also mentioned by Emily on the Prom Night episode.
I was a little shocked to think he was A because he honestly looks nothing like a DiLaurentis and he does not appear to look older than Jason even though he should because he is supposed to be 15 months older than Jason is.
He does meet the criteria however for being weird and shady. Taking him out of the show since last season would also be a clue point to that he is A because he would be someone most of the fans wouldn’t expect.
It just seems like he faded into the background yet he is mentioned on and off making sure that we as fans don’t forget him entirely. He always seemed to be wanting to get revenge in the episodes that he was in, so this would be going along with that state of mind for his character.
I am not sure if I am right about my theory but it’s just as good a theory as to who A is as anyone else’s.
Theory by Sher England.