James Earl Ray, 70, Killer of Dr. King, Dies in Nashville
James Earl Ray dies at Columbia Nashville Memorial Hospital while serving 99-year sentence for assassination of Rev Dr Martin Luther King Jr; he was 70; Ray had been treated for liver disease for last two years; Tennessee Correction Dept attributes his death to that illness and kidney failure; Ray pleaded guilty to King assassination in March 1969; he maintained for next three decades that he had been 'set up,' and used as decoy by conspirators who included mystery man he knew only as Raoul; Ray's quest to stand trial gained momentum in last year of his life, with members of King family saying they believed in his innocence; photos (M)