Hardest Investigations
Assassin's Creed's most challenging Informer, Pickpocket, Interrogation and Eavesdropping missions. Each done in a unique style.
Informer: I created a survey and found that this Informer mission in Acre is regarded as the hardest one in the whole game. All of the ones with five assassination targets are challenging. The key is to use the Hidden Blade in LOW PROFILE (release the Right Trigger) and move swiftly toward your next target before the body hits the ground. It doesn't matter if you stab them in the front or back. They won't block your blade. Other guards who find your dead bodies will become "Informed" and will draw their swords. Your witness indicator will chirp red when there's an Informed guard with a clear line of sight to you. When that happens, just don't cause a commotion like bumping into someone and you should be fine. Be careful not to walk right up next to an Informed guard (i.e. one with his sword drawn) without Blending.
Pickpocket: This one in Jerusalem is clearly the hardest in the game. All the Trouble Makers in the courtyard make it difficult to pickpocket quickly. Then the subject slips out through a guard post, complicating your pursuit. I kill the Templar for a dead body distraction. Another strategy is to throw an archer into the courtyard before the mission, scaring away the Trouble Makers. The easiest way is to unlock (Left Trigger) from the Saracen, climb out of the tower, and resume your pursuit outside.
Interrogation: You rarely need to follow your subject to a secluded location. Usually you can begin punching and/or throwing a despot immediately. Not this one in Damascus. Begin by following him away from the guards. It takes 5 throws or 9 punches landed (or some combination thereof) to win the fight. Throws are nice because they cannot be blocked and you can direct the fight. If any Thugs interfere, throw them in the opposite direction and they will walk away. I find it easier to grab and throw when NOT locked on.
Eavesdropping: Some people have trouble figuring out how to get into and out of this church anonymously. Save a citizen to the west and the Scholars will get you in the door, but they will leave and not help you get back out. I use a dead body distraction to get in and another one to get out. There are solo guards positioned nicely to facilitate this strategy. Just be careful of the Informed guards after they find the bodies.