I've been thinking. In episode 8.01 "Indelible" the flashbacks to 9/11 showed Flack in uniform. In episode 1.17 "The Fall" Flack mentioned that he worked patrol in the Bronx for four years. He would have worn the uniform then. In episode 5.10 "The Triangle" Flack stated that he worked on the Bank Robbery Task Force for four years and was a detective for seven years. That means if canon is consistent (and it's SO NOT -- it's looser than FanFiction sometimes) then he would have been on the task force during 9/11. I realize television isn't reality, but do the guys in those kinds of positions in real life wear uniforms or are they in plain clothes even if they're just officers? Of course, maybe he was working overtime as a patrol officer that day. What do you think?