The investigative process by which one tries to establish the identity of a random person who has been their facebook friend for so long that they no longer remember when or where they met.
Frequently characterized by looking up mutual friends or digging through email archives.
Guy 1: Why have you been in your room for so long?
Guy 2: I'm trying to figure out how I know this Brittany chick.. she's so hot!
Guy 1: Well she's your Facebook friend, where did you meet her?
Guy 2: I don't know man, that's what I'm tryin' to figure out! I'm doin' Facebook forensics. I found her original request in my Gmail from February 2007, and our mutual friends go to State. We musta met at that crazy Valentines Day lingerie party.
Guy 1: Why didn't you just ask her?