Wow, long take. I didn't want "much the same" to bear a lot of meaning. In the german inquisitorial system, in a criminal case, the judge takes over the (police) investigation from the prosecution. When the police become aware of a possible crime, they inform the bureau of the state attorney. A state attorney is responsible for the investigation and for uncovering the truth. But once the case goes to court, the responsibility goes to the judge.

In a civil suit, the parties are basically in charge and not the judge. It's true that the judge has a more active role in German civil procedure. While the court is not supposed to run its own investigation, it can request additional evidence if it's necessary to judge the arguments of either side. I am not clear on the details. Where matters of fact must be determined by an expert, either party can request the court to provide one. But they can also make their own arrangements. The court can also solicit an expert opinion on its own, if necessary. Typically, the expert's opinion is given as a written statement. An oral disposition may happen when questions remain. Afaik, it's unusual to depose an expert without having first requested a written statement. Either party or the court may question the witness.