3x12 Synopsis and Still Frames: Who is the Betrayer?

Sorry, it's extremely late, but here is the 3x12 synopsis and also the many still frames for the episode as well - exciting stuff is surely ahead!

"Emily is caught in the crossfire when Maya's murderer is revealed in "The Lady Killer," the mid-season finale of ABC Family's hit original series "Pretty Little Liars," 

"With Garrett's trial for Maya's murder starting, the town of Rosewood has become a media spectacle. At odds with her friends over Paige, Emily doesn't know where to turn when the media attention becomes too much for her. "A" sees this as a perfect opportunity and takes advantage of the situation and sends Aria, Emily, Hanna and Spencer on a path to a possible truce. But is "A's' peace offering real or just a trap for a much darker ending? 

Meanwhile, Aria, Emily, Hanna and Spencer are betrayed as someone very close to them is revealed as part of the "A" team. "

What do you think is to come in the 3A finale, and who shall betray the Liars?