The off-duty officer was taken into custody but later released Friday night after an argument that witnesses say got out of hand.
The victim says the off-duty officer showed his gun and made threats after an argument at a local supermarket.
Collingdale Police responded to a report of a suspect with a gun at the Aldi on MacDade Boulevard just after 6:00 p.m.
Police say several witnesses made calls to 911.
"The allegation is that the off-duty officer indicated he was armed, there was an overt movement made towards the victim and statements made to the victim," said Collingdale Police Chief Bob Adams.
Adams said the argument started in the store's checkout line.
The officer and the victim, who do not know each other, began arguing. Witnesses say it got heated and spilled out into the parking lot.
The off-duty officer allegedly lifted his shirt to show his weapon and made threats.
"At that point outside out of camera range, came the allegation of the threat with the weapon and/or display of the weapon, we don't know at this point," said Adams.
It is not clear if the gun was the officer's police-issued weapon.
The investigation has moved to the special prosecution unit. So far, no charges have been filed.