Okay, everyone I have a little theory.
Marlene said that in S5 one of the characters would find out who A is and give the audience a huge clue. I have been waiting for it this entire season and I believe I picked it out of the fatal finale.
In Holbrook’s absence this season everyone has been wondering where he’s been, what he’s been up to. This whole time I figured it was because he was cooking something up. He was onto something big and he has been working on it this whole season, hence his M.I.A.
Now, here is the clue-
“You’ve made quite a mess.” -Holbrook “I’m just curious. When did it all start?” -Holbrook “What?” -Aria “The lies, the cover ups, the murders…” -Holbrook
This clearly tells me that Holbrook is the character who discovers A’s identity, and this is his clue for us.
Holbrook has been behind the scenes this entire season and the first person he personally questions is Aria??? He seeks her out and Radley and confronts her. This obviously tells me (and this is what I already know) that Aria is A and he is on to her.
Nice work, Detective Holbrook.