Revealing mistake: In Frank and Sarah's first conversation her headset is on mute, shown by the fact it's blinking red. (00:02:25)
Revealing mistake: Alexander Dunning tells Agent Cooper to handcuff Frank. After Cooper handcuffs Frank it then cuts to a close-up of Frank's hand, showing Cooper giving him the key to the handcuffs. In this shot, we can see that the cuffs aren't actually locked in. He obviously is supposed to have locked the cuffs since he gave Frank a key to unlock them - if he faked it, why the key? This is most noticeable when Frank clenches and lowers his hand after being given the key, giving away the loose cuff. (01:41:25)






Chosen answer: He's ex CIA and considered R.E.D. (Retired and Extremely Dangerous). This is not just because of his fighting skill, but because of his knowledge and access to resources and how to use them. He just broke into the CIA Headquarters as well and is a skilled agent from another era. It is easy to assume he used his resources and experience to find Cooper's family just by seeing Cooper's face. He would easily known how to find out his identity.
Quantom X ★