(CBS) – A 54-year-old security guard at a south suburban high school died Thursday after attempting to help break up a fight between two female students.

The incident occurred shortly before 1 p.m. at Thornwood High School in South Holland. Popular security guard Richard Cowser collapsed after he and another officer tried to intervene during a fight between two girls in a school highway.

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The stricken guard fell against a school locker and appeared to have difficulty breathing, police said.

“Everybody kind stepped back all at once and I just saw him there on the ground – I was like, ‘Okay, that doesn’t look right,’” witness Abiel Sparkman tells CBS 2’s Brad Edwards.

Another witness, Javon Hall, said Cowser’s face turned blue. A faculty member reportedly performed CPR, but police said Cowser was pronounced dead at Ingalls Memorial Hospital at 1:30 p.m.

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An autopsy is pending to determine cause of death.

District 205 officials would not comment beyond saying the district is cooperating with police. The students involved in the fight and witnesses were being interviewed.

Chief Greg Baker didn’t close the door to a criminal inquiry, but added: “We won’t know until we have all of the facts. We also have to find out form tomorrow’s autopsy what the cause of death is on this gentleman.”

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Students described Cowser as a likeable man who enjoyed his job. He was nicknamed “Hulk Hogan,” they said, because of his resemblance to the wrestler.