YA! & Caught in the Crossfire cited:
Hundreds of studies have now demonstrated this contagious nature – even across many types of violence. The research shows that when an individual is exposed to violence as a victim or witness – in their community, at home or in war – they become more at risk of developing violent behaviors. The brain is picking up the violence it sees and copying it, much like the Aids virus replicates in a person.
-from Why We Need to Treat Violence Like a Contagious Disease