John Demjanjuk is fit enough to remain in custody at Germany's Stadelheim prison, officials said Wednesday, but it still could take up to two weeks for Munich prosecutors to determine whether the 89-year-old is healthy enough to stand trial. Demjanjuk is being held on suspicion of acting as an accessory to the murder of 29,000 people as a Nazi guard at the Sobibor death camp. If doctors at Stadelheim found Demjanjuk to be unwell, the retired Ohio autoworker could have been transferred to a hospital. Demjanjuk's son has said his father is dying of leukemic bone marrow disease and claimed he would not survive a trans-Atlantic flight. Dramatic photos last month showed Demjanjuk wincing in apparent pain as he was removed by immigration agents from his home in Seven Hills, Ohio, during an earlier attempt to deport him to Germany. However, images taken only days earlier and released by the US government showed him entering his car unaided. Anton Winkler, a spokesman for Munich prosecutors, said Demjanjuk "did fine" during his first night in prison and was doing well under the circumstances. "There were no problems whatsoever," Winkler said. "He is still fit enough to remain in custody." Demjanjuk's lawyer, Guenther Maull, told The Associated Press that a Munich court had rejected his challenge to the arrest. Asked if he was contemplating a new attempt to quash the warrant, Maull said they would have to consider it. "At the moment we have nothing," he said. Demjanjuk arrived in Munich on a private jet Tuesday after being deported from the United States. A medical expert is going to observe him and make a recommendation on the trial, a process that could take up to two weeks. "We are nowhere near that," Winkler said. Demjanjuk, a native of Ukraine, says he was a Red Army soldier who spent World War II as a Nazi POW and never hurt anyone. But Nazi-era documents obtained by US justice authorities and shared with German prosecutors include a photo ID identifying Demjanjuk as a guard at the Sobibor death camp and saying he was trained at an SS facility for Nazi guards at Trawniki. Both sites were in Nazi-occupied Poland. He first gained US citizenship in 1958. The US Justice Department first moved to revoke Demjanjuk's US citizenship in 1977, alleging he hid his past as a Nazi death camp guard. It was revoked in 1981. Demjanjuk was tried in Israel and found guilty in 1988 of war crimes and crimes against humanity but the conviction was overturned by the Israeli Supreme Court. That decision came after Israel won access to Soviet archives, which had depositions given after the war by 37 Treblinka guards and forced laborers who said "Ivan" was a different Ukrainian named Ivan Marchenko. His US citizenship was restored in 1998. However, a US judge revoked Demjanjuk's citizenship again in 2002 based on fresh Justice Department evidence showing he concealed his service at Sobibor and other Nazi-run death and forced-labor camps from immigration officials. A US immigration judge ruled in 2005 he could be deported to Germany, Poland or Ukraine. Munich prosecutors issued an arrest warrant for him in March.