RIVERHEAD - ? Cops say a teenager has been charged with pulling the trigger in two separate shootings in Riverhead. Cops say Juan Soyos Pixtun, 18, shot a man in the arm outside a convenience store on West Main Street last week. Police caught up with Pixtun after they say he shot another man in the leg last night at the intersection of Pulaski Street and Marcy Avenue. This morning, Pixtun was arraigned on attempted murder and assault charges.No motive has been released in the shootings.