(AP Photo/Brynn Anderson, File) In this Feb. 15, 2018, file photo, Alana Koer, of Parkland, Fla., shows text messages she received from her son the day before, during the shooting at Marjory Stoneman Douglas High School. Koer's son Kai Koer, survived the attack by Nikolas Cruz, a former student who was charged with 17 counts of premeditated murder. Modern technology has enabled real-time reaction, support and calls for action during deadly mass shootings in the U.S. Live video of the Florida shooting showed survivors under desks while others live-tweeted messages to the survivors.