An Aldan Borough police officer shot and killed a man early Thursday morning while responding to a 911 call, authorities said. When the officer arrived, he encountered a man who was armed with a knife, police said. During the encounter, the officer deployed a Taser before drawing his gun and firing at the man, police said. The officer was taken to Mercy Fitzgerald Hospital to be treated for minor injuries. Aldan police said the officer has been placed on administrative duty pending the outcome of an independent investigation by the Delaware County District Attorney's Office.