Eric:

The officers of the surrendered U-boats were sent to Washingon,
DC for interrogation by the FBI; the crews were temporarily kept at
The U.S, Navy brig (later named Correctional Facility) at Portsmouth, NH until they could be transported to the Charles Street jail in Boston, MA. They were then transferred to POW camps throughout the south. After the interrogations were over, the offivcers were sent to Boston as well.

Remember, that there were several U-boats that surrendered to U.S. Navy authorities in Portsmouth; U-234, U-805, U-873, U-1105
U-1228 and perhaps more.

Fritz Steinhoff was beaten during interrogation sessions in Portsmouth, and after arriving at the Charles Street jail he was
regularly beaten in his cell at night by one of his "jailers,"

He confided with Johann Fehler, CO of U-234, who was in a nearby cell, that if this brutality didn't stop he would end his life.

One morning later, as the prisoners stood at attention behind their
cell doors, they noticed a pool of blood coming from Steinhoff's cell. Their German doctor attempted to save his life, but failed.

When Steinhoff was searched for any type of weapon, his "jailers"
failed to check his "ditty bag" containing his sunglasses. He broke
the lenses an slit his wrists and bled to death in his cell.

This event is described vividly in the book "DYNAMITE FOR HIRE" by A.V. Sellwood - 1956.

Hope this helps,

ROBERT M.