Which reminds me, and leads me to retract my previous change of mind on this matter...Seriously, you need it explained? Just look at the "Of Mice & Men" example again. Did Lennie mean to kill Curly's wife? No, did she die, yes, was it a heinous crime? No. Was it a tragedy? Yes. Do the math.
How many times in "Of Mice and Men" did Lennie kill an animal unintentionally?
Or at least, was it often enough to make mention of it in the narrative?
Seems to me like that was one of the main themes throughout the book.
So Lennie was known to kill creatures, even if unintentionally, if he lost control.
Once Lennie killed a person, Curly's wife, a judge would have looked at his past, and recognized that Lennie was a danger to those around him, because of his (yes, unintentional) killing of animals, and now a woman, and he should have been put to death, not by George, but by Curly.