But it was also said:

You can't want the person dead as an instrumental value on the way to some positive future consequence, you can't cast it if you believe it's a necessary evil, you have to actually want them dead for the sake of being dead, as a terminal value in your utility function.

Killing the troll was for the greater good so this might not count as soul-cracking murder. But then there's also 'giving himself over fully to the killing intention' which might count.