Father James Chesney was the 'prime suspect' after nine people, including an eight-year-old girl, were killed and 30 injured when three car bombs exploded in the quiet Northern Ireland village of Claudy in July 1972.
The police chief wrote a letter which began an official cover-up, enabling the suspected terrorist to evade justice and move across the border to the Irish Republic, where he died from cancer eight years later at the age of 46.