Twenty-one people were shot dead in May by an 18-year-old gunman using two AR-15s in Robb Elementary School, Uvalde, Texas. Local funeral homes are overwhelmed and it will take weeks to bury some of the 19 children and two teachers killed. Children who were trapped near the gunman called 911 several times, begging for help. But police waited inside the school for about an hour before confronting the shooter.

Why didn't policemen break in? What were they waiting for? Dr. Qiao Liang reveals the facts behind it.