They Call Him The Vigilante
Complete every Investigation
Xbox has been having some issues in the past 2-3 days where achievements that should have unlocked ended up not unlocking as intended. I would recommend completing one investigation and see if the achievement unlocks for you.
It seems strange to me that in 360 an achievement does not explode, I have all the investigations completed, in fact I had to start act 3 only for two of missing humans and after killing the guy I only got that achievement, I don't understand what I should do, this game has me very disgusted