Make sure that you go to the Assassin's Bureau first. Talk with the guild leader there and listen to what he tells you. He will direct you to the newly opened area of the city and give you clues to where you should begin your investigation.
Note: It is very important to scale the view points in the new area and begin synchronizing.
Once you begin the synchronizing process check your map and new investigation items should appear. If you have already scaled them, climb them again and the icons should pop up on your HUD.