28 June 1976
In January 1976, a group of 100 mercenaries crossed over from the Democratic Republic of the Congo (then Zaire) to Angola in order to support The National Front for the Liberation of Angola (FNLA) in their struggle against the Government of Angola. Angola had achieved independence from Portugal in 1975 and at the time was being governed by the Popular Movement for the Liberation of Angola (MPLA). The MPLA was, not assured of governing Angola, as it was competing with the FNLA and National Union for the Total Independence of Angola (UNITA) in what became known as the Angolan Civil War. The MPLA Government was substantially supported by the Soviet Union and received considerable support from them in the form of weapons, training as well as direct military assistance from the thousands of Cuban troops stationed in Angola. One of the reasons for this was that the MPLA was a left wing political organisation, while FNLA and UNITA, were anti-Communist. This meant that during the height of the Cold War, the West supported the FNLA and UNITA. The goal of the mercenaries was the overthrow of a Communist supported government in Angola. Upon their arrival, the mercenaries set about conducting numerous raids and acts of sabotage against the Angolan people and the Government in Angola. The mercenary troupe and their FNLA allies were no match in material or training to the Soviet and Cuban soldiers and they were eventually cornered and 13 of the mercenaries, 10 British and three Americans were captured. After a trial, in Luanda, Angola, sentencing commenced on the 28 June 1976. Three British mercenaries and an American were sentenced to death, with the remaining captured mercenaries were sentenced to between 16 and 30 years in jail. Those sentenced to death were Andrew McKenzie, John Barker, Costas Georgiou, and Daniel Gearhert. The sentence was carried out the very next day. George Banks, the man who recruited them in the United Kingdom, expressed no regret for his part in the events.
References

'1976: Death sentence for mercenaries', [online], Available at: news.bbc.co.uk [Accessed 21 June 2010]|'Michael V. Scovetta: Mercenaries', [online]. Available at: www.scovetta.com [Accessed 21 June 2010]|Mercenary [online], Available at: en.academic.ru [Accessed 21 June 2010]|'Mercenaries: Lawful Combatants or War Criminals', [online]. Available at: https://www.zaoerv.de [Accessed 21 June 2010]|'The Killing of Colonel Callan', [online]. Available at: www.cvni.net/ [Accessed 21 June 2010]