Uvalde police were trained to quickly confront an active shooter. So why did they wait?

In that time, 18-year-old Salvador Ramos fired more than 100 shots while as many as 19 police officers stood outside waiting and desperate parents tried to break victims out of the school windows. It has been reported that one teacher and several children placed 911 calls while the gunman was inside the building.

The reasons for the delay in entering the school remain unclear, and the police department has been criticized for its failure to adequately explain the events, releasing contradictory reports in recent days.

The officers on duty had received active shooter training just two months before the massacre, prompting questions from parents, politicians and public safety officials about exactly what officers should have done and casting doubt on how effective such training is in reality.

It was 11.31am when law enforcement first received a call saying someone had crashed their truck across the road from Robb elementary school, and was now approaching the building with a gun.

The first officers arrived to the school parking lot just minutes later, and three officers followed behind Ramos, getting grazed by gunfire in the process. They did not continue to pursue him. By noon, 19 officers were on site. Reasons given as to why it took another 50 minutes to kill the suspect have differed, depending on who has given the account.

So what should have happened?

Police officers trained to deal with active shooting situations have frequently been criticized for not going in quickly enough; for mis-assessing the situation; or failing to prevent more bloodshed.

The Uvalde training manual lists lessons learned from Parkland, Florida, where an officer on duty drew huge public criticism and was ultimately suspended for waiting outside while the attack went on.

But the line between active shooting events versus hostage situations often blurs, as the training manual notes. The attacker might take victims hostage first, then start firing, or the active shooter situation can quickly turn into a hostage situation after the rampage has calmed.

At the Pulse nightclub shooting in Orlando, Florida, in which 49 people were killed, the gunman held several victims in a bathroom, where they texted and called 911, claiming the gunman had explosives. Eventually officers broke into the bathroom, but they were also criticized for not acting quickly enough.

But if the same mistakes are made repeatedly, they cast doubt over the efficacy of active shooter drills and police training in the face of gunmen armed with military-style weapons.