Due to its violent nature, many consider the Shooter game genre to be a representation of real world violence. Debate regarding video games causing violence were exasperated by the 1999 Columbine High School massacre, whose perpetrators, Eric Harris and Dylan Klebold, were fans of the game "Doom." Similarly, in Germany, school shootings such as those at Erfurt, Emsdetten and Winnenden, resulted in conservative politicians accusing violent shooter games, most notably "Counter Strike", of inciting young gamers to run amok. Several attempts were made to ban the "Killerspiele" (killing games) in Germany and the European Union. Shooter games were further criticized when Anders Behring Breivik, perpetrator of the 2011 Norway attacks, claimed that he developed target acquisition skills by playing "". This has led to a plethora of experimental research to determine the true effects. Experimental Research, focusing on the short term effects, found that playing violent games can increase the player's aggression. In a 2011 Supreme Court case involving a California law, Justice Antonio Scalia stated that there was some correlation between violent video games and increased aggression, but very little real-world effects. An experiment by C.A. Anderson and K.E. Dill, in which they had undergraduates randomly play either a violent or non-violent game, determined that the students who played the violent game were more susceptible to primed aggressive thoughts. Further studies have shown that there are some limitations with the research. Many research studies have not taken into account that violent video games tend to be more competitive, have a higher playing difficulty, and are more fast paced than non-violent games. Past research also shows that the way aggression was measured in the studies could be compared to the way competitiveness is measured, leaving the question of whether or not the effects of violent video games are forms of aggression or competitiveness.