(CNN)A security guard at a Family Dollar store in Flint, Michigan, was shot and killed after telling a customer to wear a state-mandated face mask, police said.

Calvin Munerlyn, 43, died at a local hospital after he was shot in the head Friday, said Michigan State Police Lt. David Kaiser.

The shooter and a second suspect remain at large, Kaiser told CNN on Monday.

Witnesses at the store told police that Munerlyn got into a verbal altercation with a woman because she was not wearing a mask, said Genesee County prosecutor David Leyton. Surveillance video confirms the incident, Leyton said.

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