The Chicopee firefighter accused of stabbing and killing his girlfriend pleaded not guilty yesterday in Holyoke District Court. Jason Chapdelaine is a 52-year-old Springfield resident who was found on South Water Street in Holyoke early Sunday morning, unconscious with what police suspected to be self-inflicted wounds. His girlfriend, Eileen Monaghan, was found nearby with fatal injuries. Monaghan, the 48-year-old mother of two grown daughters, was also Hampden County Sheriff Nick Cocchi’s executive assistant, and had worked as chief of staff for retired state representative Joseph Wagner. On Tuesday, Sheriff Cocchi and several other members of the Hampden County Sheriff’s department sat in the courtroom during the arraignment to show support for Monaghan’s friends and family. Chapdelaine was held without bail and has been placed on unpaid leave by the Chicopee Fire Department. He is next scheduled to appear in court on May 13th.