Double-killer John Gallagher told a court that he was in fear of his life when his estranged brother threw a stone through the windscreen of his van.
John Gallagher appeared at Falcarragh District Court, sitting in Letterkenny, to give evidence as the only witness in the case against his brother, Donal.
Gallagher shot his ex-girlfriend, 18-year-old Anne Gillespie, and her mother Annie, 51, in the grounds of Sligo General Hospital in 1988.
He was tried for murder but was found to be insane. He escaped from Dundrum Central Mental Hospital twelve years later and moved to Strabane, Co Tyrone, but returned to hand himself in in May 2012.
Donal Gallagher, aged 52, of 2 Hillhead Road, Urney in Strabane, was charged with criminal damage at Main Street in Lifford on October 27, 2012.
John Gallagher told Judge Paul Kelly that he had been travelling to Lifford that day to do some shopping for his mother when he observed Donal travelling in a silver Vauxhall Vectra car behind him.
He told the court that he had been subjected to a campaign of intimidation by his brother and was in fear of him so decided to change his route.
CCTV taken from a camera in John Gallagher's van was used in evidence in the case and showed him performing a U-turn at the entrance to Lifford Greyhound Stadium.
He then pulled in behind his brother's car on Main Street and Donal Gallagher was seen getting out of his car and picking up a large heavy rock before throwing it towards the windscreen of John Gallagher's van "with brutal force".
Under cross examination by defending solicitor Kieran Dillon in relation to the 1988 killings, John Gallagher said he believed that the matter was concluded and that he had done nothing wrong since that "unfortunate incident".
Judge Kelly said it was clear that the "very unfortunate history" between the two brothers "gave rise to this tension and bad feeling". He added that the CCTV footage captured with great clarity the charge undertaken by Donal Gallagher.
"There was nothing defensive in his actions but it was more an offensive manoeuvre," the judge added.
He bound Donal Gallagher to the peace for twelve months on his own bond of €500.
A compensation order for €521 for the repair of John Gallagher's van window was also ordered. Leave was granted to appeal.