Deuteronomy 20
10 When thou comest nigh unto a city to fight against it, then proclaim peace unto it.
11 And it shall be, if it make thee answer of peace, and open unto thee, then it shall be, that all the people that is found therein shall be tributaries unto thee, and they shall serve thee.
12 And if it will make no peace with thee, but will make war against thee, then thou shalt besiege it:
13 And when the LORD thy God hath delivered it into thine hands, thou shalt smite every male thereof with the edge of the sword:
14 But the women, and the little ones, and the cattle, and all that is in the city, even all the spoil thereof, shalt thou take unto thyself; and thou shalt eat the spoil of thine enemies, which the LORD thy God hath given thee.
15 Thus shalt thou do unto all the cities which are very far off from thee, which are not of the cities of these nations.
16 But of the cities of these people, which the LORD thy God doth give thee for an inheritance, thou shalt save alive nothing that breatheth:
17 But thou shalt utterly destroy them; namely, the Hittites, and the Amorites, the Canaanites, and the Perizzites, the Hivites, and the Jebusites; as the LORD thy God hath commanded thee:
18 That they teach you not to do after all their abominations, which they have done unto their gods; so should ye sin against the LORD your God.
19 When thou shalt besiege a city a long time, in making war against it to take it, thou shalt not destroy the trees thereof by forcing an axe against them: for thou mayest eat of them, and thou shalt not cut them down (for the tree of the field is man's life) to employ them in the siege:
20 Only the trees which thou knowest that they be not trees for meat, thou shalt destroy and cut them down; and thou shalt build bulwarks against the city that maketh war with thee, until it be subdued.

Deuteronomy 21
1 If one be found slain in the land which the LORD thy God giveth thee to possess it, lying in the field, and it be not known who hath slain him:
2 Then thy elders and thy judges shall come forth, and they shall measure unto the cities which are round about him that is slain:
3 And it shall be, that the city which is next unto the slain man, even the elders of that city shall take an heifer, which hath not been wrought with, and which hath not drawn in the yoke;
4 And the elders of that city shall bring down the heifer unto a rough valley, which is neither eared nor sown, and shall strike off the heifer's neck there in the valley:
5 And the priests the sons of Levi shall come near; for them the LORD thy God hath chosen to minister unto him, and to bless in the name of the LORD; and by their word shall every controversy and every stroke be tried:
6 And all the elders of that city, that are next unto the slain man, shall wash their hands over the heifer that is beheaded in the valley:
7 And they shall answer and say, Our hands have not shed this blood, neither have our eyes seen it.
8 Be merciful, O LORD, unto thy people Israel, whom thou hast redeemed, and lay not innocent blood unto thy people of Israel's charge. And the blood shall be forgiven them.
9 So shalt thou put away the guilt of innocent blood from among you, when thou shalt do that which is right in the sight of the LORD.