A firefighter in Wisconsin was shot and killed in the line of duty after responding to a medical call on Wednesday.

The male, whose name has not yet been released, worked with the Appleton Fire Department for 14 years. He was shot along with three other people, one of whom was a police officer, while at the Valley Transit Center, which was the scene of the medical emergency, according to reports. 

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In a statement, Meghan Cash of the Appleton Police Department said that while treating the person, the incident escalated into shots being fired.

“It was a very quick scene. ...We had to get people to the hospital quickly. So we’re just happy we could get them there and get them the medical attention they needed,” she told ABC affiliate WBAY.

Witness Tori Mourning said, “I saw the guy shoot a female, and she went down." She added, "... another shot was fired, and there was another male, and he went down, and then I saw the shooter flee."

It is unclear if anyone has been arrested for the crime. Police are still trying to determine what led to the shooting.