There’s no way they would have used Schroder for such a role unless they knew for sure he was politically “reliable” — there must be a lot more behind the scenes to know about Schroder and his possible/likely relationship to the Stasi and/or Soviets.
Willie Brandt’s personal aide, Guillaume, was a Soviet/East German spy. Even “TIME or “Newsweek” magazine had a big expose’ on this in the 1970’s or more likely the early 80’s.