CHICAGO (CBS) — Just days after taking cover as a gunman opened fire at their school, seniors at Dixon High School celebrated graduation, and paid tribute to the school resource officer who protected them from the shooter.

Hundreds of students, parents, and faculty gathered for commencement on Sunday, just four days after suspected teenage gunman Matt Milby allegedly stormed his former school with intent to do harm.

School resource officer Mark Dallas is credited with stopping Milby from that attack.

The hero school resource officer attended the school’s graduation, his first public appearance since the incident. The man credited with helping them safely get to this day led the march into the Dixon High School gymnasium.

More than 180 graduates received diplomas, but Dallas received as many hugs, cheers, and souvenirs as a measure of thanks for stopping a school shooting before it could turn deadly.

Wednesday morning, during rehearsals for the event, shots were fired at the school. Rather than practice walking across a stage, students were instead lining up outside in a very real crisis.

Dixon senior Matthew Milby is accused of opening fire in the school.

Dallas ran towards the danger, shot the 19-year-old, and stopped the threat. Dallas’ own son, Joshua, was one of the students rehearsing for graduation that day.

Dixon Mayor Liandro Arellano Jr. said security was enhanced for the graduation ceremony, to keep those attending at ease.

“One of the things that’s becoming very clear, unfortunately, to anyone who’s paying attention, is that the era of considering schools off-limits is over,” he said.

At Sunday’s ceremony, many graduates’ caps were decorated as reminders of the danger they faced just days earlier. One cap bore the message, “we are survivors,” and another was labelled, “because of the brave, we are here today.”

Graduating students said they could only imagine if the shooting had escalated further, as another shooting did in Santa Fe, Texas, just two days after the incident at Dixon High School. A student at Santa Fe High School has been charged with killing 10 people and wounding 10 others on Friday.

“I know they went through more than we did, but I do definitely understand now how traumatic that is,” graduating Dixon High School senior Ashley Jones said.

She and more than 180 of her classmates are well aware they’re walking away with diplomas and their lives.

Contrary to initial reports that Milby was a former student, Dixon Public School District officials said Milby was still enrolled at Dixon High School, and had earned enough credits to graduate. While he was officially part of the graduating class, his name was not read at Sunday’s ceremony, out of respect for the students who experienced the shooting.