In mercy - Tradução em português
"This is a most peculiar provision. It has been described by the government as a mandatory life sentence. But it is no such thing. To our mind a mandatory sentence is a sentence which the court is obliged to pass, like the mandatory sentence of life imprisonment for murder, which the court is obliged to pass, even when the defendant has killed in mercy.
"Out of mercy" is another possibility.
"kill in mercy" - "matar por compaixão' - cometer eutanásia.