A detective who was assigned to the case of missing Donegal schoolgirl Mary Boyle has revealed he believes she was murdered by a local man called in as a suspect at the time of her disappearance.

Speaking in a documentary 46 years after the six-year-old vanished in 1977, an unnamed garda expressed their regret at the little time they’d had to question the suspect who had been brought in for questioning.

Scannal: The Disappearance of Mary Boyle aired on RTÉ in Ireland on Tuesday evening and featured interviews with officers on the case, as well as Mary’s identical twin sister Ann Doherty.

As the mystery of ‘Ireland’s Madeleine McCann’ remains unsolved nearly half a century after Mary was last seen, the documentary explores the theory that police may have been closing in on someone who could explain what happened to her – but interference from politicians halted their efforts.

‘If I had another hour with him he may have broken,’ one cop told the program, as reported by the Irish Times.

Scannal: The Disappearance of Mary Boyle explores the disappearance of the 6-year-old schoolgirl in 1977 which remains unsolved to this day

Elsewhere in the documentary, Mary’s twin sister Ann Jr speaks about the toll her disappearance took on the family, which has been ‘pulled apart’ in the years that have followed. 

Ann said she still speaks to her sister in times of strife, to find solace and guidance.

Ann Doherty, Mary’s twin sister, has previously revealed she thinks her sister was murdered by someone known to her 

Gerry Gallagher, Mary’s uncle, was the last person to see her alive on the day she disappeared. He died earlier this year

‘In my head, I always talk to Mary, and if I’m in trouble, I’m kind of asking her for help,’ she said. ‘I always feel she’s looking out for me.’ 

Ann has previously claimed she knows who killed her twin sister and that it was someone known to Mary. 

Mary Boyle disappeared the day after St Patrick’s Day, in 1977. The six-year-old was outside her home playing with Ann, her older brother Paddy, and two cousins. 

Her uncle Gerry Gallagher, who was the brother of Mary’s mother Ann Sr., had come to the house to carry out repairs. He was using a ladder he had borrowed from the Cawley family, who lived a five-minute walk away.

At around 3.45pm Gerry left the Boyle home to return the ladder to the Cawleys. According to his account, Mary, who was eating a packet of Tayto crisps, followed him until he asked her to turn back because they had come to a waterlogged patch of field. He then said he chatted to the Cawleys before returning to his sister’s house at 4.30pm. 

It was around this time that Ann Boyle realised her daughter was not outside playing with her siblings and cousins and she began to panic.

In 2011, Mrs Boyle told the Irish Independent: ‘I looked out the front door. The rest of the children were playing in a thicket in the front garden, Mary was not there.

‘My brother Gerry was fixing a stone wall in front of the house. I asked him did he see Mary, he didn’t answer, he must not have heard me.

‘Ten minutes later I asked did anyone see Mary and Gerry shot off in his car down the road.’

At the time of Mary’s disappearance in 1977, Mrs Boyle is reported to have said: ‘When I looked out and saw only the four children, Gerry was there at the wall.

‘Gerry didn’t mention to me at any time that Mary was missing and didn’t tell me that she was with him until the first search was carried out.’

Nearly 46 years on, the case remains unsolved with no one ever charged over Mary’s disappearance. She is presumed dead but her family, including her twin sister Ann Doherty, still have no answers. 

Another theory that has circulated around Mary’s disappearance is that she fell victim to child serial killer, Robert Black.

Gerry Gallagher, the last person to see Mary alive, died earlier this year, sparking an outpouring of anguish from amateur sleuths who have followed the case for years in a bid to find out what happened to Mary.

After the news broke, Facebook users who suspect Gerry killed the six-year-old have called for Gardaí to search his land in the hope of finding her body to solve the decades-long mystery. 

One person on the Justice for Mary Boyle Facebook page wrote: ‘I am fuming that he didn’t have to face justice on this earth or reveal where Mary is.’ 

Others commented that ‘the truth goes with [Gallagher]’, noting that the missing girl’s family is still without answers.’

One person said: ‘I’m so sorry that you didn’t get to see him face justice for Mary and you for your continued fight for her. He will face his retribution for not letting her rest peacefully.’

Another wrote: ‘If he knew something I hope he left a note. If he was guilty, God will be the judge now!

‘Let’s hope Mary is found soon enough.’

In 2016, Ann Doherty spoke to investigative journalist Gemma O’Doherty as part of a documentary about her twin sister’s disappearance.

Appearing in Mary Boyle: The Untold Story, Ann said: ‘I believe that Mary had a secret. And, because Mary was fiesty, Mary would have told.

‘So I believe Mary had to be killed, to stop her from telling.’

When asked by the journalist what she thought the secret was, Ann replied: ‘Mary was sexually assaulted.’

Mary’s sister has previously shared her suspicions with the gardaí. No details about the suspect were aired on the podcast at the time for legal reasons, but it was understood at the time that she was referring to Gerry.

Ann called for an inquest into her twin’s death but Mrs Boyle disagreed, arguing she did not want to admit Mary was dead.

At the time Mrs Boyle said: ‘I don’t want an inquest that Mary is dead. I want to believe that Mary is still alive somewhere. I have to live that way.’