Also, remove any sheetrock that is damaged. This will need to be done anyway to change any insulation that gets wet. Basically wet insulation looses up to 50% of it's r-value forever.
And you do not want to grow any mold because it does not dry correctly.
You will also see the hidden damage, but not necessarily where it is originating. To find the problem, you may be removing some siding as Oldog suggested. This will lead you to where the weather barrier and flashing have failed....basically someone tucked their raincoat into their pants.