Informer

Informants are fellow members of the Assassins' Order who can offer you aid in your investigations of your assassination targets. However, before you can get this information from them, you have to complete a small task for them. Informants can be found within the three cities of Assassin's Creed by climbing View Points.

Tasks
Before revealing their secrets to you, Informants will ask something in return from you, like assassinating some guard who's been after him or escorting him out of the city.

Flag Collecting
An Informant may test you, by asking you to collect flags. This is to be done within three to five minutes. Then, you must return to the Informant.

The flags will always be placed in a path, not randomly. Sometimes, this path will bring you to a flag other than those for the test, like a Templar or Hospitalier flag. It is highly recommended that you have your GPS enabled while performing this task.

Templar Assassinations
Sometimes, your comrade will have angered a knight, or a group of knights. Fearful for their life, they will offer to give you information if you assassinate the offending knights within a set time limit. In addition, you must not become Exposed- if you become exposed even once, even if only for a second, you fail the mission. Once all targets have fallen, return to your Informant.

You must either use your Hidden Blade or Throwing Knives to complete it. If a knife hits, it always kills a knight. Beware of rooftop archers. On the PC version of the game, 4 more Investigation mission were added. Those are listed below and are avaiable on the PC version only

Informant Escort
Dangerous as it may be, an informant may ask you to escort him to a exit of the city safely instead of in a body bag in exchange of information. It consists of simply accompanying him through a path and repelling any attacker before they can kill him. Reaching the city's gates, the informant will provide you the info and leave the town.

Merchant Destruction
In order to stop the monetary influx of your target's bank account (medieval-tenth-century-like bank account), your informant asks you to destroy some merchants tent. The way to do it is grab someone passing by and toss them into the stand. These could be done either with citizens or guards, with the respectives consequences taken, like loss of synch by killing civilians (which may not happen, if the unfortunate throwed just falls unconscious) and/or being attacked and pursued by guards.

Archers Assassinations
Performed similarly to the templar's murder task, but with different reasons. Your pal the informant needs to get to someone or something, but there are archers in his way that should not have been. So its up to you to take them out and make his task a little easy. In exchange of it, he gives you the informations you need.

Rooftops' Run
One informant that don't have the information may redirect you to another informant which in turn have the information. He gives the location of the guy and the player must run through the rooftops to reach him in time. Falling or running on the ground doesn't fails the mission, but usually takes longer.

Trivia
When approaching an Informant with the Hidden Blade, it is possible to assassinate him. If you don't resist the urge to kill him, just getting way out of the the location and coming back a short time later will make him respawn.