Let's step back from the school violence, the video games the parents, politicians, etc..
How can anyone say:"violent games are effecting adolescents minds" when ALL around them is a deluge of violence on the streets. By both perps and police. Violence from bullies, violence from parents and family. Horrifying violence overseas. All out military interventions are currently being executed a several locations all over the world.
In a controlled experiment, we would first have to remove all of the above to determine if video games were the cause of violence in adolescents.