CHICAGO (CBS) — Dixon High School Resource Officer, Mark Dallas, is speaking out following the Dixon High School shooting on May 16.

The resource officer’s actions saved countless lives when a shooter walked into the school. Dallas confronted the gunman during the incident. When the suspect fired shots, Dallas shot back, injuring the gunman.

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CBS 2’s Roseanne Tellez is the first Chicago reporter to sit down and talk with Dallas.

“We heard several shots in the hallway,” recalled Dallas. “I don’t even know what I yelled, but I yelled at the top of my lungs.”

Seconds later, Dallas was running down the hall of Dixon High School, exchanging gunfire with the shooter.

19-year-old Matt Milby, the alleged gunman, was shot and wounded before he could reach the gym where Dallas’s own son was rehearsing for graduation.

“I have a hard time just thinking about it because I run the ‘what if’s’ through my head,” said Dallas.

Dallas will be honored for his heroics in Springfield Wednesday, where he hopes to deliver a message about the importance of school resource officers. He says they serve students in many ways.

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“If they have a problem at home or a situation on social media, I deal with that whole gamut of stuff,” Dallas explained.

He says he feels like he had 192 kids in the gym that day.

“It’s unfortunate, we have evil people who do evil things sometimes,” said Dallas.

Dallas’s son, Joshua, recalls reuniting with his father after the shooting.

“I just gave him the longest hug I’ve ever given him before. It was a rejoicing moment,” said Joshua Dallas.

Matt Milby, whose mother says he was bullied at school, is facing three counts of felony aggravated discharge of a weapon.

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Mark Dallas plans to return to his job at Dixon High School in the fall.