Stone was stopped at the door of Stormont in November 2006
Michael Stone has denied he was an "egocentric killer...who was completing unfinished business".
The loyalist killer is on trial for the attempted murder of Gerry Adams and Martin McGuinness in Stormont in November 2006.
Stone said that, before the Good Friday Agreement, one of his "biggest regrets" was not killing the two men during his attack at Milltown cemetery in 1988.
The 53-year-old denies the attempted murder charges and 12 other charges.
Stone also admitted to the court that, when he was an active loyalist paramilitary, he had been part of a plan to assassinate former London mayor Ken Livingstone - at the time the leader of now-defunct Greater London Council (GLC) - and had even gone on "two dry runs" before the operation was aborted.
He confessed the plan had been to disguise himself as a jogger, to use a gun to shoot Mr Livingstone "once in the head and twice in the body", before running along the Thames embankment and throwing the murder weapon into the river.