( CNN ) -- A Massachusetts police dog searching for a handgun not only found the weapon but fired it with his paw , a police chief said Sunday . No one was injured when K-9 search dog Ivan discharged a bullet as he indicated the gun 's location , Lawrence Police Chief John Romero told CNN . `` Everyone on the scene was startled , including Ivan , '' Romero said with a chuckle . The search for the weapon began after a police officer on patrol early Saturday morning was responding to hearing three gunshots , according to Romero . The officer followed a vehicle , which sped off . A short time later , a passenger in the rear seat exited the vehicle and ran to a nearby snow bank to bury something . The passenger re-entered the vehicle , and the officer stopped it but waited for backup before ordering the three men out of the vehicle , Romero said . After the men exited the vehicle , Ivan 's handler , Essex County Sheriff 's Lt. John Pickles , commanded the dog to search for a gun after a shell casing was found in the backseat of the car , Romero said . Ivan is trained `` to paw '' if he finds something . `` I surmise that the snow was there for a week , and it was probably like ice , '' Romero said . `` The individual probably was not able to bury it very deep , and he had no time . '' After Ivan recovered and fired the weapon , the three men were arrested and charged with possession of a firearm , possession of ammunition , receiving a firearm with a defaced serial number and receiving stolen property , Romero said . The individual believed to have buried the gun was also charged with discharging a firearm within 150 feet of a highway and carrying a firearm without a license . The semiautomatic Ruger was stolen from New Hampshire in October 2012 . As of Sunday , all three were being held in jail and awaiting a Monday arraignment , Romero said . CNN 's Rob Frehse contributed to this report .
A Massachusetts sheriff 's search dog finds and fires a gun . `` Everyone on the scene was startled , including Ivan , '' police chief says . Three men are now charged with firearms violations , police chief says .