Sheppard performs a quietus (mercy kill)

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Anything where John has to prepare for (or actually carry out) a quietus on someone he's responsible for? Spare them from being eaten alive by ants or tortured to death or interrogated for intel that absolutely cannot be leaked, that kind of thing. I like McShep for maximum angst potential, but other targets are good too (the more innocent the better - civilians? children? Jeannie McKay's children? Torren?). It doesn't have to be the main plot of the story, as long as John is seriously prepared to do it.

I have a death-fic tag on this request, but I like happy endings as well as angsty ones. Both older and newer stories welcome.