I think it is the easy access to guns.It is easy to point and shoot without giving it a second thought.Take away all firing weapons and see the crime rate go down quickly.It is a lot more difficult to kill someone in a fist fight,and less likely to happen because of the energy needed.

This is a good discussing Q. You can't name just one reason, as satisfying as that would be, it is impossible. Assuming no real mental disorder, I would have to say the most sweeping reason would have to be "want." The want of something such as money, goods, or even happiness such as incidents where people kill spouse or family member due to unhappiness in the relationship. Now what seperates those that deal with their needs/wants in a socially acceptable manner, and those that don't is a whole other discussion. There have been countless papers and studies done on the matter, and my own personal conclusion is that violence is hard-wired into our mind. Some are better at ignoring it than others, but many seem to take delight in the suffering of others. This is of course the the minority, but still none the less, I feel it is in the mind of all, some deeper down than others. Read up on the Milgrim experiments, and you can get a taste of people's reaction to the idea of hurting or even killing an individual. The study really had more to do with how people follow authority, but you can see reactions of people to others pain as well. As for stopping it, I feel murder will never be completely rid of until you rid people of their "want."

Big Time Mental Illiness - for people to pay attention to mood changes in their faimly and friends and see if we can open up to them befor it gets out of hand

It is the environment which a person is raised that can determine how they commit socially offensive behaviour. You are NOT born to kill. You pick that up within the society or how you were conditioned. Studies have shown that most serial killers have had a traumatic childhood or something of that nature. If you were taken as a baby and raised by buddhist or taken and raised by a poor african village, how different will things be, you'd have deferent values and incentives. As to fixing it, you would have to eliminate the causes of this behaviour by designing a different society and value system. You cannot prevent this in the current system as this system forces us to compete with each other in order to survive and has bulit in corruption. I've learnt this from, thevenusproject.com & thezeitgeistmovement.com (social change)

Its usually caused by deep boiling hate for one another or race or people. It can even because of demon possession (Even if you don't believe in it).