Rabbi Kahane apparently wrote that every Jew should have enough Torah knowledge to be a qualified rabbi.
It seems clear that in Laws of Injury and Damages, he refers to the law that an empowered Jewish court could give the death sentence. In Laws of Kings 10:6, Rambam cites the rule that a Noahide court cannot execute a Gentile who strikes a Jew, despite his liability to death by the hand of God.