On 24 January 2014, Downey appeared at the Old Bailey for the beginning of his trial; he entered a not guilty plea on the four murder charges and the charge of intending to cause an explosion. On 25 February 2014, it was revealed that Downey's trial had collapsed after the presiding judge had ruled, on 21 February, upon a letter sent by the Police Service of Northern Ireland to Downey in 2007, assuring him that he would not face criminal charges over the attack. Although the assurance was made in error and the police realised the mistake, it was never withdrawn, and the judge ruled that therefore the defendant had been misled and prosecuting him would be an abuse of executive power. Downey is one of 187 IRA suspects who received secret on-the-run letters guaranteeing them unofficial immunity from prosecution. In December 2019 the High Court ruled in a civil action against Downey by the family of a victim that he had been an "active participant" in the Hyde Park bombing, subject to a claim for damages.