HARTFORD, Conn. (AP) — Federal authorities are investigating a Connecticut gun-maker after agents found nearly 3,000 assault rifle parts missing serial numbers, according to recently filed court documents. Bureau of Alcohol, Tobacco, Firearms and Explosives agents seized nearly 300 of the AR-15 parts from Stag Arms in September following routine inspections, prosecutors said. At the time, the father of Stag Arms owner Mark Malkowski told authorities that the employee who places serial numbers on parts was on vacation. The New Britain-based gun-maker gained a high profile in the state when Malkowski became a vocal critic of a stricter state gun-control...