Martin McGuinness' brother William told Eamon Collins [whilst both were in prison] that several IRA men had been wounded on Bloody Sunday and were evacuated across the border. One of the men was secretly buried and his family given an alternative story. Collins said he'd heard loads of dodgy rumours down the years but considering who it came from[and he said it quite matter of factly] is cause to give credence to the claim. Collins did not include it in his book Killing Rage as he was terrified of retribution. He rightly anticipated the media would focus in on that bombshell, undermining the Provies narrative about Bloody Sunday. It didn't matter, Collins was brutally murdered near his home walking his dog with a spike driven through his face numerous times.
