County Donegal in Ireland is about to have its bucolic image shattered by a report into how paedophiles, both clergy and laity, abused children for decades.

An investigation into clerical sex abuse in the Catholic diocese of Raphoe in County Donegal is about to report its findings, which are expected to be damning. Meanwhile, new evidence has emerged from victims of a parallel paedophile ring operating in the same Gaelic-speaking corner of the Irish Republic.

A number of survivors of abuse have told the Guardian that lay members of the church as well as priests sexually exploited them for years in the county.

And as with the expected conclusion of the report into Raphoe, they say the national police service, the Garda, was complicit in a culture of cover-up that allowed the perpetrators to carry on abusing them.

Speaking for the first time about his abuse as a child and the subsequent cover-up, John O'Donnell revealed that he had been abused since he was nine by a lay member of a local church choir.

"He assaulted me from when I was nine until I was 15, until I was old enough to know it was wrong. This man took advantage because I was adopted and regarded as something lower than most kids in the area.

"The abuse took place at his home and in a shop he ran. It went on from 1965 to 1972."

O'Donnell said that in 1973 he went to a local Garda station to report that he had been raped by the man, who has since died. He said the reaction to his claim was violent.

"A local guard was outraged that I was naming such a fine upstanding member of the community as a child rapist. The officer slapped me on the face and told me to get out. He said to me that I was adopted and not worth anything. From that day on I never fully trusted a member of the Garda Síochána."

For years, O'Donnell said, he hid what had happened to him, and got married and raised a family without discussing it with his loved ones. It was only in the late 1990s when revelations of widespread child abuse rocked the Irish Catholic church that he decided to face up to what had happened to him.

"I found out that my abuser was still in the church choir and I was outraged because he was working with children. So I drove up to a parochial house in the area and tried to speak to the parish priest about this man. At the time I had finally got somewhere with the gardaí and they had questioned this man in a Donegal police station. I informed the parish priest about this but he wouldn't even let me across his door. He kept saying: 'No, no, no … I am not speaking to you about this.' He didn't want to know, and bear in mind this was only back in 2005."

O'Donnell has claimed that other victims in this corner of Donegal are coming forward, with a picture emerging of an organised paedophile ring. Police are investigating their claims.

The Guardian has spoken to a number of other men in Donegal who have made similar allegations of an abuse ring and a cover-up spanning decades.

Throughout the decades of denial, the young men who were preyed upon by paedophiles in the county, both inside and outside the church, had one champion – a retired police detective, Martin Ridge.

Ridge moved to the county at the end of his career, and became so disturbed by official indifference that he wrote a book about the children's experiences, Breaking the Silence.

He predicted that the Raphoe report would be "damning" and expose the same culture of "local denial and cover-up" that was found in other Catholic dioceses across Ireland.

Ridge admitted the police force he served in all his working life would not be spared withering criticism in the Raphoe report. Two years ago the Murphy report into widespread clerical abuse of children in Dublin, Ireland's largest Catholic diocese, found that senior Garda officers colluded with four archbishops and top clerics in covering up the sex crimes of priests on a massive scale in the city.

"There were 45 victims of three different paedophiles, one of whom was a priest, another a school teacher. None of the victims wanted to be interviewed in local gardaí stations. The question has to be asked as to why they did not trust the local force when this was going on," Ridge said.

The ex-Garda officer too has confirmed that an investigation is now under way into the alleged ring of abuse in north-west Ireland involving both priests and non-members of the clergy. It is understood to include an investigation into how a convicted child sex offender got a job in a local youth hostel after he was released from prison in 2006.

O'Donnell, meanwhile, opted to remain living in Falcarragh, County Donegal, despite the climate of cover-up and fear he has had to endure.

Surveying the natural beauty of the area, with its stunning mountains and seascapes, the 55-year-old said: "Yes, it's a beautiful area with amazing views and scenery … it would be even more beautiful but for some of the bastards still living here."