FERGUSON, Mo. – A security officer fatally shot a gunman at a Ferguson gas station overnight after an argument led to an exchange of gunfire.

The shooting happened around 1:30 a.m. at a Ferguson QuikTrip in the 10000 block of West Florissant Avenue. Investigators have not yet disclosed the identity of the security guard or suspect involved.

The Ferguson Police Department says the incident unfolded shortly after the suspect tried to make a purchase and there was “an apparent disagreement over required identification for the transaction.”

The suspect left, then quickly returned to the store. Shortly after that, an altercation arose between him and an on-duty security officer.

According to surveillance footage reviewed by police, the situation escalated to the point that both the suspect and the security officer pulled out firearms. An exchange of gunfire followed.

The suspect was fatally shot at the scene. The security guard was also shot, but while wearing a bulletproof vest. He suffered non-life-threatening injuries and was released from the hospital Saturday morning after treatment.

The St. Louis County Crime Scene Unit and Ferguson Police Department are investigating the shooting.