On 22 June 1922, Dunne and Joseph O'Sullivan murdered Field Marshal Sir Henry Wilson in London. Dunne managed to escape, but O'Sullivan was captured by an angry crowd. He had lost a leg in World War I. When Dunne returned to try to help his friend, he was also captured after shooting and wounding two police officers and a passer-by. The event provided the inspiration for the film Odd Man Out.
On trial, Dunne addressed the jury about how in the recent Great War he had been "fighting for the principles for which this country (the UK) stood. Those principles I found as an Irishman were not applied to my own country…"
Dunne wrote a speech which he was prevented from making from the dock (reprinted in the Irish Independent 21 July 1922). In it he blamed Wilson for the "Orange Terror", as the Military Adviser to the Belfast Government who had raised the Ulster Special Constables. and went on to say:
- "... We took our part in supporting the aspirations of our fellow-countrymen in the same way as we took our part in supporting the nations of the world who fought for the rights of small nationalities... The same principles for which we shed our blood on the battle-field of Europe led us to commit the act we are charged with."
- "You can condemn us to death today, but you cannot deprive us of the belief that what we have done was necessary to preserve the lives and the happiness of our countrymen in Ireland. You may, by your verdict, find us guilty, but we will go to the scaffold justified by the verdict of our own consciences."
He was found guilty after three minutes. Both men were hanged for Wilson's murder at Wandsworth Prison on 10 August 1922 and buried within the prison grounds. In 1967, Dunne and O'Sullivan were reburied in Deans Grange Cemetery, Ireland.
- Jeffery 2006, p. 284.
- An Phoblacht article