Ok, I've just read this story. I liked it more than expected (because I don't care too much for westerns or for Luccio). A few comments (SPOILERS!!!)
I think Luccio considered that setting the place on fire wouldn't be "killing by magic". That doesn't mean there is not a law against that.
About what you were discussing before about McCoy, perhaps he was the Blackstaff and the Captain at the same time, but Luccio didn't know he was the Blackstaff
I agree about how suspicious it it that Kemmler left her skin behind. It smells trap.
I wanted to see Karl set free, his work done. Also I believe he could have been used better.
No dying curses from the bad guys? It seems too convenient. Also I clearly remember Harry several times thinking that a bullet is very efficient against dying curses but that is a modern concept that most old wizards in the Council didn't gatther. Still, Luccio had it very clear in this story
I was angry "someone" saved her in the end. She had done a lot, she deserved to save herself.