EVEN in the brutal context of the IRA's terrorist offensive against the British 30 years ago, July 20, 1982 stands out as a particularly barbarous bookmark in recent history.
That morning, 16 members of the Blues and Royals regiment of the household cavalry and their horses, along with two mounted police officers, were passing from Knightsbridge Barracks to Horse Guards Parade for the changing of the guard ceremony.
On South Carriage Drive was a blue Morris Marina, registration number LMD 657P, containing a bomb made up of between 20 and 25 pounds of high explosive surrounded by wire nails.
When it went off, Lieutenant Anthony Daly (23) and Trooper Simon Tipper (19) died at the scene. Lance Corporal Jeffrey Young (19) died the following day and Squadron Quartermaster Corporal Roy Bright (36) died two days after him.
Seven horses were destroyed and 31 people were injured.
The car had been bought a week before at a car auction in Enfield, north London, by a man with an Irish accent who gave false personal details.
A photofit of the man who planted the bomb was published in the media and in May 1983 it was circulated on the police national computer system that Downey was wanted for conspiracy to murder.
The 'Sunday Times' published a picture of Downey in 1984, saying he was on the top of Scotland Yard's most wanted list.
The prosecution in the case argued that Downey's appearance in 1982 was consistent with photofits prepared by three witnesses and his fingerprints were on parking tickets connected with the car used in the bombing.
In 1989, Britain's then attorney general, Patrick Mayhew, held a meeting about the possibility of seeking the extradition of Downey. It was agreed that with the lapse of time in the case and the standard of the evidence, they would not seek extradition.
Fast forward almost 24 years and Downey was arrested at Gatwick Airport, on his way to Greece, and charged with four murders and doing an act with the intent to cause an explosion. He pleaded not guilty to all the charges. Two hours after the bomb had exploded in the blue Morris Marina, another bomb went off underneath the bandstand in Regents Park as the Royal Green Jackets played music from 'Oliver' to 120 spectators. Seven people were killed in the second bomb.