Someone will always be influenced by something - whether it be games, movies, books, or even stories. I don't think games cause crime (thousands of virtual kills in COD4, yet I don't even own a gun, nor do I need one in the area I live). But even if they did - so what? Outlaw any book, film or game that depicts any violence whatsoever? There's a ton of bloodshed in the Bible - and some people have actually said the bible inspired them to kill (these people are usually insane to begin with). Do we ban the Bible? No, of course not. And that's why we shouldn't ban games either, even if they did cause crime (and there is no indication that they do).

There have been serial killers, murderers, robbers, thugs, throughout human history. In ANY population, throughout time, there has always been a minority of human beings who commit violent crimes. Always has been, always will be. In actual fact, crime in the US and many other nations has gone DOWN over the past decade, yet because the media reports crime all the time, people's perception of violence has increased.

Why do people do evil things? I don't know. But what I do know is that criminals/murderers have existed ever since the human species has existed. There will always be a small minority of people who kill, and they will always be inspired by something, games, books, films, or whatnot.