Band at the execution

[BettyO]

According to Silent Sentinel on the Potomac, Fort McNair 1791-191, by Phyllis McClellan, in 1871, there WAS a hospital building on the post (pp. 55-57), designated as "Building 17B."

This was post-war. Nothing regarding a hospital in 1865 - still searching....
The same source states that one Brevet Major George Ramsey commanded the post from 1858 to 1863 when Major James D. Benton was appointed Commander. He remained until 1866. I would therefore supposed that Hartranft was simply appointed Commander while the conspirators were housed there.