Dumbest dorf moment I've seen yet.
So I have a Tower of Justice -- it's a tower of stairs built on top of one of my towers that goes to the very highest z-level. There's a cage next to a pit area. Captured goblins and the like get taken up there and thrown off as reparations for every ambush, siege, etc, that I encounter.
So I get a siege, which nets some caged goblins. I assign them all to the cage at the top of the Tower of Justice, and one by one, they get trundled up.
Very soon after this, I get another siege -- maybe 1 or 2 months apart. So I round up the defenses, and then set the "dwarfs stay inside" order.
The battle goes smoothly, with me only losing three dwarves, who I figured got stuck outside of the defenses. Afterwards, I'm doing mop up, and then I go up to the tower of justice to assign the new captives.
I notice a dead dwarf corpse up there, at z-level +15. I think, that's odd. I review the announcements, and see that the dwarf is one of the three that I lost -- it shows that he'd been shot.
Now, at the very top, the Tower is just a single tile wide, and it has no walls, so I'm thinking, "Jesus H. Christ, those must've been some bowmen to get a shot off like that!"
But then I look at the announcements again, and see a few items up before dying, "Ast Odgubrimtar, Leatherworker, cancels Large Creature Caging: Forbidden area".
And it clicks. The Tower has no roof. He was transferring one of the prisoners, got to the top of the tower, realized he shouldn't be outside, cancelled the task, and the prisoner he was transferring then calmly shot him in the back as he ran inside.
The prisoner then descended the stairs back into the fort, resulting in the other two killings before being put down.
*Sigh*