Michael Stone, a loyalist terrorist, was found guilty yesterday of attempting to murder Gerry Adams and Martin McGuinness in an armed attack on the Stormont parliament in Belfast.

Stone, 53, a former member of the Ulster Defence Association (UDA), was convicted at Belfast Crown Court over the incident in November, 2006, when he entered the building, while the Assembly was in session, armed with explosives and other weapons. He had claimed that his action was “performance art”.

That defence was described by Mr Justice Deeney as being “wholly undeserved of belief”. He said that defence evidence that Stone had been taking part in some sort of a “comic parody” was “hopelessly unconvincing” and “self-contradictory”. After the verdict was read out, Stone, dressed in a denim jacket and jeans, shouted from the dock: “It is another concession to the Shinners [Sinn Fein].”

He was also convicted on seven other counts, including the possession of nail bombs, three knives, a garrotte and an axe, as well as causing criminal damage to the Stormont building. He is due to be sentenced next month.

During the 4½-week trial his lawyers argued that the weapons were all “props”, while letters sent by Stone to two journalists outlining his intention to kill the two senior republicans were also part of his “script”. The piece of interpretative theatre was designed to expose the hypocrisy of local politicians.

Crown prosecutors dismissed the theories, accusing Stone of using them to explain away his true intentions.

The judge said that he was satisfied with the evidence of explosives experts that the nail bombs and incendiary devices carried by Stone were viable and could have caused death.

The incident happened on the day that Ian Paisley, of the Democratic Unionists, and Mr McGuinness, of Sinn Fein, were due to be nominated as Northern Ireland’s new First and Deputy First Ministers.

Stone, who was released from prison on licence under the terms of the 1998 Good Friday peace agreement, was born in 1955 in Birmingham but moved to Northern Ireland when he was still an infant. He was brought up on the Braniel estate, a working-class loyalist area of east Belfast.

His nickname at Lisnasharragh High School, which George Best attended, was “Flint”. This, he claimed, was because of the tough attitude that regularly led to him being thrown out of class. From the age of 14 he trained as a cadet soldier. He got work as a “hammer boy” in the blacksmith’s shop at the Harland & Wolff shipyard but claimed that he was forced to leave after tackling a bully.

By the age of 16 he had joined the UDA and was trained by its leader, Tommy Herron. He claimed that he was taught to kill with a punch to the heart and never to trust anybody. Mr Herron’s death in 1973 was attributed by some to members of the UDA.

Stone was regarded as a hero by his comrades for killing three mourners in a solo gun and grenade attack on an IRA funeral in 1988. When charged with the Milltown Cemetery murders, he told police that he was responding to the IRA’s “slaughter of innocents”. The bullet-proof vest that he wore was auctioned for £10,000 in a loyalist club in Scotland.

He was rescued by police as a republican mob closed in on him, but sentenced to 684 years imprisonment. He took up painting and on his release from prison became an artist, selling his works for up to £30,000.

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