David Moran, a criminal law professor at Wayne State University, commented about the renewed police interest in interviewing accused murderer Stephen Grant's au pair, Verena Dierkes, who has returned to Germany. Lawyers said there is no way Macomb authorities can legally require Dierkes to return to the area or to work with local investigators. \"Foreign witnesses can only get here voluntarily,\" Moran said. \"You can transmit a subpoena to somebody overseas and ask him or her to show up, but it\'s up to them.\"