“Quantico” is finally wrapping up one mystery in the midseason finale. The ABC drama will reveal who the Grand Central bomber is, and the answer is bound to shock fans. The show has made it clear that someone started framing Alex (Priyanka Chopra) when she arrived at Quantico. So which of her classmates will be revealed as the terrorist in the winter finale? Check out our best theories:

Shelby: While Shelby (Johanna Braddy) seems pretty wholesome, she clearly has some secrets. Her “sister” is still extremely suspicious. Though Shelby seemed to break down when she found out that her sister was an imposter, it seems odd that she didn’t fully investigate before. Could she have been putting on an act for Caleb (Graham Rogers)? Plus, she told Alex that she discovered tons of family secrets after her parents died on 9/11. What were they hiding? Her discoveries could have led her down a dangerous path.

Caleb: There is a lot of anger in Caleb. He seemingly always had a strained relationship with his father, and he is mad at Shelby for having an affair with the director. That doesn’t seem like enough to bomb Grand Central station, but Clayton (Mark Pellegrino) also revealed that his son was once in a cult. Perhaps his father didn’t actually save him from the manipulative group, and they convinced Caleb to help bomb Grand Central.

Elias: There wasn’t much reason to be suspicious of Elias (Rick Cosnett) -- until he chloroformed Simon (Tate Ellington) in last week’s cliffhanger. Even if he isn’t guilty of planting the bomb, he is definitely guilty of something.

Raina: While infiltrating a terrorist cell, Raina (Yasmine Al Massri) apparently developed feelings for one of the leaders. She even visited him in the hospital while they were supposed to be tracking down leads to help Alex. When Raina's twin sister Nimah (Yasmine Al Massri) confronted her about it, Raina tried to defend the man and said he doesn’t really want to hurt anyone. Her feelings for the criminal may have led her to help plan the attack. 

Brandon: Where is Brandon (Jacob Artist)? He has been at “Quantico” plenty, but he is one of the only NATs viewers haven’t seen in the flash-forwards yet. Even though he doesn't seem to have much motive, his absence is definitely suspicious. 

Who is the bomber on “Quantico”? Take the poll below:

Anyone who was at Quantico with Alex could be the bomber, but only one option has been firmly eliminated. Showrunner Joshua Safran previously said that when a character says they’re telling the truth, it is indeed the real deal. Simon said he wasn’t the terrorist and explained he was working with bomb makers to make a political statement, not to actually kill people. It looks like Simon is not the bomber. 

The “Quantico” Season 1 winter finale airs Sunday at 10 p.m. EST on ABC. Do you have another theory about who the terrorist is? Sound off in the comments section below!