Too many stories to tell.
Okay, one of my favourites: BND knew the whereabouts of Adolf Eichmann. They were actively hiding that from the Israelis, since they were worried an Eichmann trial would give away too much about the nazi career of German Kanzleramtsminister Hans Globke. BND even tried to meddle with the Eichmann trial once it started. (German state prosecutor Fritz Bauer helped the Israelis to find him, but he had to do this in secret, because, well..., the Germans spied on him.)