I would like to think sattelite images/tracking would give an idea of where the missile was launched from.
I wonder tho if russia have those missiles that got banned, they invented some missiles that could go in space, orbit the earth for as long as they like without fuel use and then re enter orbit near the target. Officially russia abandoned those missiles, but unofficially who knows.
Makes you wonder about the Stars Wars programme. All ICBMs go into space and then use stellar mapping to fix their pre-determined co-ordinates.