It is understood that envelopes from the letters may still exist - raising the possibility they could provide a DNA profile of the hoaxer through saliva traces.
The journalist was an experienced Twitter hoaxer, having previously posted fake tweets about the death of the pope and Fidel Castro and established a number fake accounts for world leaders.
The hoaxer, who had an accent said to be from the Castletown area of Sunderland, sent police three letters and an audio tape at the height of the Yorkshire Ripper inquiry in 1978 and 1979.