A Rockland accused of killing his ex-girlfriend has pleaded not guilty to murder.Arnold Diana entered that plea Thursday in Knox County Superior Court in Rockland. Police say Diana strangled 47-year-old Katrina Windred of Friendship in his apartment November 20th while her 11year-old son sat in her car reading comic books. Police say Diana wrapped the body in a blanket and then dumped it on the side of a road near on the outskirts of town. Windred’s body was found three days later by a man walking his dog. Diana was arrested November 27th and has been held without bail since then.