I wasn't aware that there was even a U-896. Are you sure you don't mean U-869 which was an IXC/40. She had gone through the 4th Flotilla Training (4 Unterseebootsflotille) out of Stettin from 1 December 1944 to 11 February 1945.
U-869 was commissioned on 26 January 1944 and went on a single patrol. 2 warships were sunk for a total of 1,960 tons. 2 other ships were damaged beyond repair for a total of 11,844 GRT. 1 warship was damaged for an additional 1,400 tons.
She was sunk with all hands 11 February 1945 off the coast of New Jersey by Hedgehogs and depth charges from the destroyer escorts USS Howard D. Crow and USS Koiner. 56 souls lost. Previously credited to the destroyer escort USS Fowler and French submarine chaser L'Indiscret 28 February 1945 off the Moroccan coast near Rabat.
This all sounds like it's your 'mystery' sub.
http://www.pbs.org/wgbh/nova/lostsub/tour.html
http://www.u869.com/
http://uboat.net/boats/u869.htm
http://www.uscg.mil/history/WEBCUTTE...ow_Koiner.html
http://www.northernatlanticdive.com/u_869.htm
