The latest mass killing in the U.S. happened Monday in Charlotte, North Carolina. Four officers were fatally shot. Another four officers were wounded. It happened when a task force of officers from different agencies arrived in a residential neighborhood to capture a 39-year-old man on a warrant for firearm possession by an ex-felon. The man also died. It was the country’s 15th mass killing this year, according to a database maintained by The Associated Press and USA Today in partnership with Northeastern University. At least 68 people have died this year in those killings. Last year was one of the deadliest years on record with 217 deaths from 42 mass killings in the U.S.