He has no memories of his mother – what she looked like, the way she laughed, how she loved him. All this he learned, years later, from relatives.

But Tony Friel does remember the funeral. Standing in the graveyard in driving rain, only four years old, as the coffin was lowered into the ground. His mother Bernadette (22) had been found in the bedroom of a house in Derry in October 1975 with a single gunshot wound to her head.

The ex-British soldier who was with her said she'd killed herself in a game of Russian roulette. As a child, Tony heard the story many times. But, like the rest of the Friel family, he never believed that. "It was very hard," he says. "The state lied about what happened to my mother.

"By claiming she had been playing this 'game' when she died, they blackened her name. And growing up in a republican area of Derry wasn't always easy either. There was a lot of name calling.

"Lads on street corners would shout, 'You're a Brit lover's son', or taunt me that my mother had killed herself. As a teenager, I got into more fights than enough over it. I always defended my mother."

Thirty-five years after Bernadette was killed and her reputation maligned, the Friels say the truth has finally prevailed. A Historical Enquiries Team (HET) report into Bernadette's death has accused ex-British soldier Thomas Ramsay of lying about her death and says he should have been charged with murder.

She was a headstrong young woman who charted an unconventional course in nationalist Derry. She was arrested twice for rioting, yet at night she'd go out with British soldiers. Her family advised her against this. "But there was no talking to her," laughs Tony.

"My uncles say the more somebody tried to tell my mother not to do something, the more likely she was to do it. She worked in a shirt factory during the day and that was dull, so at night she longed for a bit of fun. There was no harm in her. She just wanted to live her life to the fullest."

At 17, Bernadette became pregnant to a British soldier. He was later posted to Cyprus but they stayed in touch. She hoped to marry him. For some reason, she never told him he'd become a father. She was due to meet him in England just days before she was killed but his leave was delayed. He never made contact with the Friels after her death.

"I don't think he even knows she died," says Tony. "When she wasn't in touch again he probably just reckoned she'd lost interest. He certainly doesn't know I exist and I've made no attempt to find him."

At 11am on 19 October 1975, Bernadette visited Thomas Ramsay's home in the Carnhill area of Derry. A local man, Ramsay had joined the British army but then left, telling everybody he'd been kicked out.

Bernadette was best friends with his wife. She was away for the weekend and Bernadette had called in to check that her three children were okay. Shortly after arriving, she went upstairs. Ramsay and his brother-in-law, Hugh Stanley (16), followed.

Almost immediately a shot was heard in the bedroom. Bernadette lay alive but unconscious with a single gunshot wound to the head. A passing British army patrol heard the shot and called an ambulance.

Bernadette died in hospital two days later. Ramsay and Stanley were initially detained by the British army in Fort George military base. Bizarrely, it was four hours before they were handed over to police.

Ramsey had hidden the weapon and the spent cartridge and, at first, lied about the incident. Later, he and Stanley alleged they'd been playing Russian roulette with a .45 revolver at Bernadette's suggestion.

During a search of Ramsey's house after the shooting, several guns were found. Detectives recommended he be charged with murder. However, on the DPP's direction, this was reduced to manslaughter. Ramsay was sentenced to 12 months imprisonment – he served eight. No action was taken against Stanley for Bernadette's death and he was given a two-year conditional discharge for the firearms offences.

Tony says: "The sentences defied belief. This was at a time when a young nationalist, found with even one gun, was getting 10 or 12 years in jail. We suspect Ramsay was treated leniently because he was a British agent, sent back to spy on republicans with the fake story that he'd been kicked out of the army."

Tony finds it "incredible" that the British army allowed Ramsay to travel with Bernadette in the ambulance to hospital: "He would have wanted to do that in case she regained consciousness and implicated him."

The HET claims Ramsay deliberately shot his victim and fabricated the Russian roulette story. The report says Bernadette's post mortem shows "the position of the wound and the direction of travel of the bullet completely excludes any possibility [she] could have shot herself".

It rejects Ramsay's story that Bernadette had wanted to play with the gun: "It is incomprehensible to consider that she would have consented to any engagement in such irrational and life-threatening behaviour. Ramsay was an ex-British soldier who would be in no doubt about the dangers associated with such reckless use of firearms. His explanation lacks credibility."

There were many irregularities after the shooting. The murder scene wasn't cordoned off. There is no record of a fingerprint examination of the weapon or the scene.

But amidst the bleakness of that awful day, there was a small act of kindness. A soldier at the scene placed a pillow under Bernadette's head. The Friels have written to him, through the HET, to thank him.

No one knows why Ramsay shot Bernadette. "We accept that he will never be charged again and my mother won't get justice but, at the very least, we'd like him to tell us why he killed her," says Tony.

He has only two photographs of his mother. In one, she's standing with him at the door of their home in Rossville flats; the other was taken on the grass beside the flats just weeks before she died. They're his most treasured possessions.

Tony was brought up by his grandfather and seven uncles and aunts: "They were brilliant but I still missed my mother so much. My first communion, Christmas, birthdays – on all those special occasions I'd have given anything for her to be there with me, even just for a moment."