Andover police and the FBI are investigating how two two rifles were stolen from a bureau vehicle parked overnight in Andover apparently by a 16-year-old Lawrence boy.During a press conference announcing the arrest of a 16-year-old for the theft, Andover Police Chief Patrick Keefe would not say how the FBI SWAT vehicle was broken into, but he said other cars nearby were also burglarized and those cars were left unlocked.