The parents had the password, the page had already been put into memorial mode by "friends" of the deceased, which blocked access.
Facebook refused to deactivate memorial mode and allow them parents access. They were taken to court and the parents lost, because the German Telecommunications Secrecy act protects private electronic correspondance.
It didn't matter, in this case, that the parents already had the passwords, the courts have said that that is irrelevant. The communications are protected by law.