Yvonne Laborda sent the link to this article: Long-term study finds zero link between violence in video games and real life
Same for "violent movies":
...No link could be made, he found, except perhaps in the mid-20th century.
At this point in history, homicide rates and instances of violent movies both increased briefly, but then the trend reversed after 1990, to the point where movie violence became correlated with fewer homicides. This was also the case during the two decades between the 1920s and ’40s.