John D. Williams, 29, pleaded not guilty to a charge of murder in the slaying of Somerset County Sheriff’s Deputy Cpl. Eugene Cole, whose April killing launched a manhunt that saw some 200 members of federal, state and local law enforcement scouring a rural portion central Maine for four days. Williams appeared in a Portland courtroom for a brief arraignment proceeding Tuesday afternoon. Since his arrest, Williams has been held without bail at the Maine State Prison.