(NewsNation) — The police response to the massacre at Robb Elementary School in Texas has been harshly criticized, as it is now known police did not overtake the shooter for over an hour as he murdered students in a classroom.

Police eventually shot and killed the gunman, but only after he killed 21 people, including 19 children.

In suburban Chicago, a gunman opened fire on a Highland Park Fourth of July parade, killing seven people while perched on a rooftop with an assault-style weapon. Police were able to hunt down the suspected shooter and take him in alive.

In Buffalo, the situation was similar. Police were able to take in a suspected gunman alive after 10 people were killed inside a grocery store.

All of those situations present different obstacles for police to look at when responding to the scene, and in each case, the execution of the police response varies in success.

Frank Straub, the director of the Center for Targeted Violence Prevention, said one thing should be the same across all police responses to mass shootings: The police need to go toward the gunfire.

“It is a given we go to the shooter,” Straub said. “The idea is to neutralize the threat as quickly as possible and then stop the bleeding.”

Straub said that is where police in Uvalde failed but also where authorities succeeded in Highland Park, Illinois.

“I think what we saw in Highland Park is a very quick reaction. The officers were trying to find the shooter, a little bit difficult in this situation because he was on a rooftop,” Straub said. “But we did see his apprehension come about fairly quickly.”

The idea of police running to the gunfire, especially in a mass shooting event, stems in particular from the Columbine High School shooting, where police waited outside the building while students were killed inside.

“The benchmark, sadly, is Columbine. It was in Columbine that officers waited outside until the SWAT team could, special weapons and tactics teams, arrived,” Straub said. “What we know from that instance is that a number of people were killed inside the school while officers were outside waiting for the SWAT team and other officers.”

By heading toward gunfire, officers will be putting themselves in danger, but in the unfortunate incident of a mass shooting, that’s part of the job.

“The first officer on scene, if they arrive and they hear gunshots, they are to go to those gunshots,” Straub said. “Clearly, it’s a very dangerous situation and officers can be killed, as we’ve seen in Colorado and other places, or they can be seriously injured.”