In the hours and days following the fatal shooting of 19 children and their two teachers at Robb Elementary School in Uvalde, Texas, on Tuesday, authorities gave shifting and at times contradictory information of what happened and how they responded.

The investigation of the massacre is ongoing, but much is already known about the nearly two hours that passed between when authorities say Salvador Ramos shot his grandmother and when police radio traffic indicated that the 18-year-old gunman was dead and the siege was over, the Associated Press reports.