After a group of gang members learned that their friend had died in a seemingly random accident, several of the friends started blaming a rival gang for the death. Even though there was no evidence...

After a group of gang members learned that their friend had died in a seemingly random accident, several of the friends started blaming a rival gang for the death. Even though there was no evidence whatsoever that the death had been intentional, the more the friends talked, the more passionate they became in their belief that an act of revenge was necessary. What concept from social psychology may contribute to an act of violent revenge in this case?