Gerhard Schindler provided ample evidence to back up his case, including satellite images and diverse photo evidence.
Now suppose that one of the satellite images showed the before launch image of a BUK launch unit and a second showed the after launch picture of the same launcher with a missile missing. If the time between images was narrow enough, it would unambiguously locate the point of launch of the MH17 responsible launcher.
We haven't seen the data that Germany has (nor are we likely to) but this type of data would be very conclusive.