Same with rioting in the north of Ireland. I grew up near a hotspot in Belfast and violence often went unreported to avoid the situation growing worse or spreading to other areas.
As a resident of the U.S. I always wonder once the headlines of the latest mass shooting appear if such events would be less frequent if they were never reported in the news.
By definition that's something that would be impossible to know.
Several sites withhold the shooters name, because often times a quest for notoriety is a goal for them. Denying this potentially removes some incentive.