The question itself is so painfully naive as to be a harbinger of hand-wringing futility. Human beings have been killing other human beings for as long as we have written records. Ancient skeletons of murdered people show that these killings went on before humans were even capable of writing. The cave men were killers, and babies born into the world today come equipped with no more morality than the offspring of the cave men. If they turn out any better, it is because morality has been inculcated into them during their childhood.
Morality is civilization's first line of defense.
Police and the criminal justice system are the last line of defense for those relatively few who are not stopped by society's other defenses. Unfortunately, there seem to be increasing numbers of people for whom morality means nothing. Some of this may be part of the general trends of our times. However, most people are unaware of how much of the breakdown of morality is not just a happenstance, but is part of a decades-long systematic undermining of moral norms by the schools themselves. Most moral principles do not require any clarification, nor is clarification what these programs offer.