Dora Bas Rivka Silver O'H
And You Thought Pilate Came Up With Washing One's Hands!
When the army approaches an enemy city, they were first to offer a peaceful solution. If the citizens of the city agreed to Israelite rule, that would be that. If they reject this offer, the alternative is to fight. God will hand the city to the Jews, but they are only to kill the men as enemy combatants; women and children were POWs. (Animals and inanimate objects were the spoils of war.)
The above only applies in the case of a milchemes r'shus, an "optional war." In the case of a "milchemes mitzvah," that is, an obligatory war against the Canaanite nations, the Jews had to utterly drive out or destroy them; one way or the other, they were not permitted to remain in the land. (According to the Rambam in Hilchos Melachim 6:1, this is only the case if the Canaanite city refuses Israelite rule.)
When the Jews wage war, they're not allowed to destroy any fruit trees. They're only allowed to cut down such a tree if the enemy is somehow using it to their advantage. A tree that doesn't produce fruit may be cut down as needed for lumber to build weapons.
If a corpse is discovered murdered by persons unknown in the fields between cities, representatives of the Sanhedrin will have to measure distances to see which city is closest. The elders of that city will have to sever the neck of a calf near a flowing stream. Those elders will then wash their hands over the calf and say that the people of their city were not responsible for the victim's death. (That is, they take good care of guests in their city, even providing an escort out of town – see Rashi, who cites Talmud Sotah 45b.) The kohanim will then ask God to forgive the people for this unsolved crime. This will atone for the victim's death.