Alright. Im gonna help you guys out with what i can. Im currently on the 5th general.
First off, ill tell how to get to the informer. Its simple. Look at your mini map, follow the sign and then climb the roof there. There will be an opening in "garden" like structure, with a door inside. Walk in, talk/argue with informer (dont forget to take the feather) and leave.
Also, so you guys know that after the first 3 generals, the minimap (and the big map) wont show you the locations of investigations. You'll have to find them yourself. I suggest forgetting about the roof tops and concentrate on walking on streets. Pay close attention to 2 people talking to eachother. It might be the "pickpocket" investigation, OR the "evesdrop" investigation. Also, whenver you hear someone talking loud (preaching to the crowd) see what he says. If he praizes the name of the target = lock on to him with left trigger, dont even think twice. Wait for him to finish, follow him somewhere dark and scary (make sure there are no thugs near by for they will attack you as well) and attack the target with FISTS, note: fists, not weapons. Beat him up untill he talks. Here is a tip to fist fighting. Hold right trigger, when the opponent hits you, let go of the trigger and press X. Do that a couple of times and they'll talk for sure.
Before killing one of each generals, I would suggest killing off the archers on rooftops and plotting the fastest way to escape. Unlike me, some people have trouble fighting 10 guards at the same time. So i suggest avoiding that conflict and running away as soon as you finish off the general. If you do like a challange and you are sure in yourself that guards wont pose a problem, then please go ahead and slaughter them. Be warned, they tend to come more and more and more.
Also, a fast way to dispatch a group of bully guards is to hold right trigger and A button, (make sure you have hidden blade selected) and charge at the first bully you see, as soon as you are about to collide with him, let go of A button and press X. You will jump on him like a crazed lion and pierce his neck killing him. After that quickly select dagger/knives and attack the closes bully to you. Most likely they wont have time to react to what just happened and you will quickly finish off the second one. 3 more to go, figure it out.