The British government is coming under renewed pressure to admit a cancer-causing gas was used on republican prisoners during a 1974 Long Kesh riot.
A prison warder on duty on the day has said that he now has lung cancer despite being a non-smoker and a non-drinker.
He also says that a number of his colleagues who inhaled the gas fired from British army helicopters have died prematurely from cancer despite leading healthy lives.
Republican prisoners have always insisted CR gas was used to quell the October 16 riot.
Medical research shows that toxins in the gas cause cancer. Unlike CS gas, CR gas is banned from use by US police forces or military because of its cancer-causing potential.
The British government admits CR gas was being kept in Long Kesh and that clearance for its use had been granted. However, it denies using it on PoWs.
A fifth of the 300 republican prisoners who were gassed have since died or are suffering from cancer.
Former IRA prisoner Jim McCann is one of those affected. The West Belfast man runs the Ceartais group, which supports the families of those inmates who have died or are suffering from cancer.
Mr McCann has urged former warders to add their voices to those demanding the truth.
He said: “With the amount of gas fired that day, I’m not surprised people who weren’t meant to be affected are now victims.
“I would urge former prison officers with knowledge of what happened to come forward.
“They worked for the Prison Service, and that’s where the answers are, they are with the Prison Service and Ministry of Defence.”
Two years ago soldiers from the Duke of Edinburgh Royal Regiment admitted that an “unknown gas” has been used.
The soldiers were sent into Long Kesh to take on the rioting prisoners.
One soldier said: “I can tell you now, because I have seen CS gas being used, that it wasn’t CS which was fired from the helicopters.
“I don’t know what it was, we weren’t told and we didn’t ask questions.”
The IRA’s leader in Long Kesh at the time, George Gillen, also said that prison chief William ‘Punchy’ Wright admitted to him that CR gas had been used. Mr Gillen, who died earlier this year, was called to a meeting with Wright in the days after the riot.
“I hadn’t even sat down when this guy started talking about CR gas,” said Mr Gillen.
“To be honest, I really didn’t know what it was he was on about.
“But he said to me, I can still remember it clearly, he said, ‘Everything I tell you is off the record. The prison officers had nothing to do with the distribution of CR gas’.
“It wasn’t until years later when the stuff about CR gas being used on us came out that I realised what he had meant,” he added.