I believe the precise location in which people were held may have depended on which allied nation operated their trials, but generally they remained incarcerated within German prisons under the supervision of allied authorities. I can provide a specific example from my own research. In the case of the Einsatzgruppen trial, held in 1947, those who were not hanged upon being found guilty remained in Landesberg prison. This included Ernst Biberstein, onetime head of Einsatzkommando 6, who was initially sentenced to death, but later had his sentence commuted to life imprisonment after a successful appeal. His time after sentencing seemed to involve doing work around the prison (in the laundry, and the library, if I remember correctly), spending some time working for the voluntary prison gardening/ botanical organization (when he could be bothered), and routinely petitioning the American authorities for clemency. He also had regular, though not particularly frequent, visits with his wife and children at the prison. He developed health issues and as a result also had regular doctor's visits within the prison. He also visited the prison pastor. In 1958, he was released along with many other convicted criminals found guilty at Nuremburg. I think Biberstein's experience of incarceration would have been similar to that of many men convicted but not sentenced to death. Those who study war crimes trials operated by other allies (France, Britain) could perhaps expand on this from that perspective. Sources: Atrocities on Trial, Ed. Heberer ; National Archives, D.C. - Biberstein's prison records.