another story. We're learning more about what happened when a gunman walked into a supermarket in indiana and opened fire. And it is the third incident this week, after that movie theater, and then,... See More
another story. We're learning more about what happened when a gunman walked into a supermarket in indiana and opened fire. And it is the third incident this week, after that movie theater, and then, the middle school. But this time, local police were ready. And abc's senior justice correspondent, pierre thomas, tells us just what they did. Reporter: Last night, police say 22-year-old shawn bayer was strolling through the martin's supermarket when he pulls out a handgun and begins shooting. He allegedly kills two women. And holds the store manager at gunpoint. You can see the manager there in a praying position. You see the shooter waving the gun at him. Reporter: Two patrolmen arrive within two minutes of receiving the 911 call. Bayer runs. Police chase them through the store. And in an exchange of gunfire, bayer is killed. The violence encounter is over in just minutes. Saved lives. There's no doubt. Reporter: Police know because of incidents like columbine, ordinary patrolmen can't wait for backup. They can't wait for s.W.A.T. They have to go in, confront. With mass shootings on the rise, the fbi is now helping local police teach quick response tactics like those used last night to cops across the country. This is an emergency that could happen not only in any town, usa, but in your town usa. Reporter: In this training scenario, a gunman is in a school. Patrolmen are caught, forget old-school. Don't just secure the perimeter. Move quickly around for gunfire. Seconds count. Hunt for the shooter. Be prepared beforehand. Have high-capacity rifles in patrol cars. Tend to wounded victims. Know, find, engage the shooter. Push you forward to stop threats. Before we'd wait on specializeunits. Now, go in and stop that shooter. Reporter: Quick action. That's exactly what happened in elkhart, indiana, last night. And another big story now.
This transcript has been automatically generated and may not be 100% accurate.