The Rite Aid on Highway 231 in Hazel Green was robbed Friday afternoon around 4 p.m.
Sergeant T. A. Miller says an off-duty police officer pulled into the parking lot, spotting four masked men walking into the Rite Aid. After calling 911, the off-duty officer said two men spotted him and ran away while the other two entered the store.
After robbing the store, the other two men walked out and one man had a gun in his hand. Both men took off and the off-duty officer ran after one man and arrested him.
Authorities are still looking for three other men.
After receiving the description of their vehicle, police have located the car and recovered a backpack filled with money stolen from Rite Aid.
Police searched through a neighborhood off Millbrae Drive in Huntsville where the suspect's car was found. Officers with K9 dogs scoured through homes on Timwood Drive and recovered one gun from the house, but it's unclear whether that gun belonged to the suspect or not.
According to Sgt. Miller, no one was injured during the robbery.
Police have a 16-year-old male in custody, but they are not releasing his name.