I have found something about those who died in Siegburg as POW:
http://www.demerath-eifel.de/kultur/images/Mahnmal_Deutsch.PDF shall be a memorial for the B-26 crews crashed in the Eifel 23th Dec. 1944.
The pilot Capt. Mont F. Stephensen was hurt and came to the Hospital in Siegburg where he died on 03rd Jan. 1945. The author describes that he contacted Stephensen's family to inform them about what he knows and about the memorial cross standing at the place of the crash.
His burial in Riverton, Salt Lake County, is mentioned here http://www.findagrave.com/cgi-bin/fg.cgi?page=gr&GRid=31042640 (another link: http://www.b26.com/marauderman/mont_stephensen.htm), burial means he is really buried there, doesn't it? So it seems as if he came home after the war, even though these pages term the 23rd December as date of his death.
The SiegburgMortuaryPhoto is made in the front court of the abbey. When you go through the bigger arched gateway you are outside of the abbey, some meters further you are at the upper end of the wall of the rose garden. Through the smaller gateway you come to stairs ending at a small platform on the wall of the abbey. I don't really know where there is a mortuary.
Christoph