I was thinking of the David Carradine Movie so I googled the actual Battle of Alcatraz in 1946. The movie was more or less faithful to what obviously transpired among the six convicts. Reading the actual case, I finally understood why the three (Coy, Hubbard, and Cretzer) had to be cut down by gunfire, while of the three who went back to their cells, two (Shockley and Thompson) were later executed. The sixth, Carnes, was clearly guiltless as far as the deaths of the two prison guards were concerned.
What I can’t understand is how they even thought their plan would work. Basically it was to disarm the guards, take their weapons, and then hold them hostage all the way to being ferried by boat to wherever they wanted to go (San Francisco?)
When the boat plan failed, they decided to hold some high ground in the island, still with hostages. At this point, one guard was already dead (Miller) so the six had already sealed their fates.
Another mystery to me was why the warden stipulated an open attack by the US Marines at the sides and roofs of the buildings, instead of rooting the suspects out through the entrances (more or less perfected during the Pacific war against entrenched Japanese troops.) The Wiki mentioned a “no-gun” policy inside the cell blocks but this was clearly a special case.