And the 53-year-old former RUC Special Branch agent is also set to name the republican who allegedly was the masked gunman who shot dead Joanne Mathers over three decades ago.
Gilmour’s updated book What Price The Truth? is due to published in two months on Amazon.
It is a follow-up to his 1998 blockbuster book Dead Ground which gave a fascinating and spine-chilling insight into his life as a secret police agent inside the IRA’s ruthless Derry Brigade.
Sunday Life has seen a number of extracts from Gilmour’s forthcoming book.
At the time of Joanne Mathers murder, the now Deputy First Minister was reportedly the IRA’s Chief of Staff but according to Gilmour, he still had his finger on the pulse of Derry and all IRA terrorist operations.
In the extract, Gilmour writes: “Nothing, and I mean nothing, happened in Derry without the say so and nod from Martin McGuinness.
“He was top of the pile. There was no one higher up the ladder than him.
“McGuinness was the power behind the throne in Derry. Everything had to be cleared through McGuinness first.
“So I can say with absolute certainty that McGuinness gave the order to kill Mrs Mathers.’’
Mrs Mathers, 29, was shot dead in Gobnascale's Anderson Crescent in Derry as she collected census forms in 1981.
At the time, Sinn Fein urged people not to complete forms to demonstrate support for the 1981 hunger strike.
The move meant officials could not collect the forms from householders in republican areas.
No-one was ever convicted of her murder and the case is currently being reviewed by the Historical Enquiries Team.
Her husband Lowry has put up a reward for information leading to the arrest and conviction of his wife’s killer.
It is understood Gilmour is prepared to risk his personal security to come to Northern Ireland and speak to HET about the murder of Mrs Mathers.
A friend said: “Raymond knows he is under threat of death for the rest of his life. Even by writing this book he fears he will be killed before it is published.
“He has held onto secrets for years and now he wants them off his chest.
“He says that even at the time of the supergrass trials, his Special Branch handler ‘Pete’ was frightened of his revelations.’’
For the first time, Gilmour will also:
n name the IRA unit who murdered Lord Louis Mountbatten, the Queen’s Cousin in Co Sligo in 1979, where it was planned and how it was planned;
n reveal how he could have saved Mountbatten but wasn’t fully aware of the operation until it was too late, writing “I was just a kid at the time”;
n accuse Martin McGuinness of involvement in the murder of two RUC officers just days before Bloody Sunday with a Thompson sub-machinegun, the same weapon the Savile Inquiry said he was “probably” carrying on Bloody Sunday in January 1972;
n that the Sinn Fein chief had a hand-picked team of Provos in Derry to carry out gun attacks on soldiers; and
n that Martin McGuinness was in contact with his mum in a bid to convince him to come home from his hideaway.
“I wasn’t going to fall for that old trick of his,’’ writes Gilmour.
“He did that to Franko Hegarty and he ended up getting a bullet in the back of his head.’’
Frank Hegarty was a member of the IRA’s Derry brigade but was working as an agent for the Force Research Unit. He gave his FRU handlers the locations of three secret arms dumps in the Republic which were located by Gardai.
However, in 1986 the IRA fingered him as the ‘tout’ and he fled to England. According to the Hegarty family, Martin McGuinness would visit ‘Franko’s’ mum Rose in a bid to convince her son would be safe if he came home.
When he arrived home, Hegarty was told by McGuinness he had to meet the IRA in Donegal to “straighten things out’’.
A few days later, after going to a hotel in Buncrana, Co Donegal, Hegarty’s half naked and rain-soaked body was found dumped along the border with a bullet in his head.
Gilmour’s book will describe his life as an RUC Special Branch agent, working in Derry’s Creggan estate against the INLA and IRA from 1976.
What Price The Truth? By Raymond Gilmour is published on April 2 on Amazon Kindle