Generally speaking, it is very hard to make connections between nutrition as a single factor and behavior (source):
One of the more difficult problems in research on diet and behavior is how to separate nutritional from non-nutritional factors. Because
food is so intimately involved with other aspects of our daily lives,
it contains much more than its obvious nutritional value. Food is an
intrinsic part of social functions, religious observations, and
cultural rituals. Because food is a "loaded" variable, both
experimenters and subjects may harbor biases about expected research
outcomes. To minimize the confounding effects of these biases,
double-blind procedures in which neither the experimenter nor the
subjects know what treatment is given must be used.
According to this source, there is no clear evidence about meat affecting behavior:
When it comes to food and behavior, there are no clear cut answers.
Meat consumption may have either positive or negative affects on
behavior, or none.
However, there are some hypotheses that link meat consumption to:
a 2011 article published in the Dartmouth Undergraduate Journal of
Science reports that food's impact on mood is individual, and may
depend on all the nutrients you've eaten, as well as time of day, age
Meat is a source of tryptophan, an amino acid and precursor to the
feel-good chemical serotonin. Low levels of tryptophan are associated
with an increase in aggression, according to a 2009 review article
published in the International Journal of Tryptophan Research.
Overall, the results are mixed and it is very hard to link meat consumption as a single factor to violent behavior. So, most certainty meat consumption only cannot be considered a trigger for violent behavior.