According to Manu, the great author of civic codes and religious principles, even the killer of an animal is to be considered a murderer because animal food is never meant for the civilized man, whose prime duty is to prepare himself for going back to Godhead. He says that in the act of killing an animal there is a regular conspiracy by the party of sinners, and that all of them are liable to be punished as murderers exactly like a party of conspirators who kill a human being combinedly. He who gives permission, he who kills the animal, he who sells the slaughtered animal, he who cooks the animal, he who administers distribution of the foodstuff, and at last he who eats such cooked animal food are all murderers, and all of them are liable to be punished by the laws of nature.

From Srila Prabhupada’s purport to SB 1.7.37