Normally reliable security sources in Derry have linked the Provisional IRA to a gun attack in the city on Sunday night in which a coach driver was shot twice in the legs.
Mr Danny McVerrity (54), was driving pensioners home from a trip to Bundoran, Co Donegal, when he was attacked as he stopped in Aranmore Avenue in the Creggan estate, at 11.20 p.m. on Sunday.
Mr David Trimble has called on the IRA to admit if it had a role in the attack. He called it "shameful and cowardly". Sinn Féin has denied IRA involvement.
Four men, dressed in paramilitary uniforms and wearing balaclavas, boarded the coach.
They struck the driver on the head with a hammer before shooting him in the legs.
One of the bullets caused multiple fractures to the victim's shin bone.
"We have no doubt that a Republican paramilitary group carried out this attack and we believe that it was planned, sanctioned and carried out by the Provisional IRA," a security source said.
Mr Trimble claimed Mr McVerrity was a supporter of Mr Joseph McCloskey who had been "exiled from Londonderry by the republican movement after he intervened in a bar-room brawl".
He added: "Human rights activists working on the McCloskey case were told some time ago that Mr McVerrity could be expected to be attacked for his stand."
He asked: "Was \ horrific attack on Danny McVerrity an attack on the McCloskeys by proxy?"
He called for the treat on Mr McCloskey's life to be lifted.
"The republican leadership in Londonderry has an obligation to make its position clear.
"The Belfast Agreement is lauded publicly by Sinn Féin, while in private its principles are held in contempt by their IRA alter egos."
Several of the five pensioners on the coach when the driver was shot, yesterday told how they took cover at the back of the vehicle.
"They stormed onto the bus and told the driver that they wanted to hijack the vehicle," said Ms Anne McDevitt.
"The next thing they were on top of the driver. We all started to scream and when we heard the first shot we ran back to the rear of the bus to take cover. Then we heard more shots.
"I looked up and saw the blood on the driver. It was terrible. I had never seen anything like that before," she said.
The Mayor of Derry, SDLP councillor, Ms Kathleen McCloskey, condemned those responsible. "We're working to keep guns out of politics and it is a sad day for our city that we still have gunmen running around ruthlessly terrorising pensioners and ruthlessly gunning a man down," she said.