An even more compelling and recent study seems to corroborate this view point. Prisoners in a correctional facility in California were given the option to eat vegan food along with anger management counseling in a program called New Start. The inmates who opted for the vegan diet had dramatic changes in behavior. Compared to the inmates not in the program, instances of violence reduced significantly, recidivism rates drop to 2% compared to the state average of 90%, and attitude changes occurred so much that the inmates no longer formed associations based on racial groups.
While this study was based on a small sample size and may also have flaws in it's design (for example, maybe the inmates who joined the program were non-violent to begin with), it does seem to support the relationship between vegan diets and reductions in violent behavior which is what we need more of in our global community.