Police say an illegal gun recovered Tuesday, after armed men robbed a fast-food restaurant, was the same weapon used to murder John Amos, nephew of operations officer for the Area Five police, Superintendent Newton Amos.

One of three gunmen who were involved in the robbery was shot and killed after a quick-response team rushed to the scene and engaged the men in a shoot-out.

The gunmen had reportedly relieved the security guard, who was on duty at the restaurant, of his service firearm before robbing patrons and cashiers of more than $300,000 in cash and cellular phones.

Police initially believed that the gun, a Beretta 9mm pistol, had been used in a number of shooting incidents.

Subsequent investigations then found it to be the gun stolen from John Amos during a robbery on July 21 at a supermarket in Linstead, St Catherine, after which Amos was shot and killed.

Investigators are also theorising that the deceased robber is among a group of men whom are believed to be behind a spate of robberies in St Catherine.

He is yet to be identified.