Assasins Creed question?

Im playing the first assassins creed. I did the first few assassinations in Damascus, Jerusalem, and Acre. I discovered all the view points and i saved every citizen and i did all the investigations in each city. Now Al mualm gave me more missions to do in those same citys, but i cant because it the bureau says to climb a view point to access investigations spots but i already discovered them all. How do i do these missions?