The families of the 21 victims of the Texas school massacre grieved after devastating loss, while calls grew in the U.S. for changing gun laws. A 18-year-old gunman killed 19 children and two teachers at an elementary school on Tuesday. It was the deadliest such incident since the 2012 Sandy Hook shooting in Connecticut. Mental health experts say the parents who lost their children risk slipping into deep and lasting bouts of post traumatic stress.