For anyone interested in studies on the effects of violence in video games a brief google revealed hundreds.
Anderson, C.A., & Bushman, B.J. (2001). "Effects of violent games on aggressive behavior, aggressive cognition, aggressive affect, physiological arousal, and prosocial behavior: A meta-analytical review of the scientific literature". Psychological Science, 12, 353?359.
Anderson, C.A., & Dill, K.E. (2000). "Video games and aggressive thoughts, feelings, and behavior in the laboratory and in life". Journal of Personality and Social Psychology, 78, 772?790.
Jansz, J., & Martis, R. (2003). "The representation of gender and ethnicity in digital interactive games". In M. Copier & J. Raessens (Eds.), Level up: Digital games research conference (pp. 260?269). Utrecht: Utrecht University.
Schie, E.G. v., & Wiegman, O. (1997). "Children and videogames: Leisure activities, aggression, social integration, and school performance". Journal of Applied Social Psychology, 27, 1175?1194.
Wiegman, O., & Schie, E.G.M. v. (1998). "Video game playing and its relations with aggressive and prosocial behaviour". British Journal of Social Psychology, 37, 367?378.