Oh, I almost forgot. You hinted that you wondered why the execution took place at Huntsville and not at Macon City where the district Union headquarters was located.
I should say up front that I don't really know for a fact, but I think I figured that out. The Union military in northeast MO captured actually scores of members of both Colonel John Porter's recruiting command and Colonel John Poindexter's recruiting command during the summer and fall of 1862 in northeast MO. The Yankee military prisons in the St. Louis area were bulging with them. The Northeast District was authorized to keep certain prisoners for military tribunals in the district, especially oath violators. The only jails available in northeast Missouri were local jails and makeshift jails. Frankly, the Union military was simply not equipped to house the large number of prisoners they captured in this region. I would guess the Union district headquarters used the civil jail at Huntsville to handle the overflow from Macon City and other jails. Call that an educated guess.