United States Congressman Brendan Boyle has pledged his support for justice for Ireland's youngest and longest missing child following a meeting with her twin sister on Capitol Hill this week.

Ann Doherty’s battle for the truth began when her 6-year-old twin sister, Mary Boyle, went missing in March 1977 on her grandparent's remote farm in Cashelard, Co Donegal. Her remains have never been found.

Doherty and senior Gardaí who worked on the case believe Mary was sexually assaulted and murdered by someone she knew and that her body was dumped close to where she went missing. She also believes she knows who is responsible for the horrible crime but that political intervention early in the police investigation attempted to cover the killer’s tracks, leaving the perpetrator to walk free.

For years the Donegal woman has worked to win justice for her sister, traveling to Westminster, Stormont and Brussels to raise awareness about the case abroad in the hope that the Irish authorities will finally act.

This week she met with members of the United States Congress to inform them that Mary's killer is being shielded by An Garda Siochana (the Irish police force) and that a politician interfered in the investigation shortly after the murder, ordering that certain people were not to be considered suspects.

Accompanied by investigative journalist Gemma O'Doherty, Doherty had a lengthy meeting with Congressman Brendan Boyle on Capitol Hill in the lead up to St. Patrick’s Day, and the Democrat from Pennsylvania, whose father is from Glencolumbkille in Donegal, pledged his support.

Wearing a Donegal tie to the meeting, Congressman Boyle offered to assist them in their search for truth and justice in whatever capacity he can, expressing particular concern that Mary's remains had not yet been found and that her killer is still at large.

"It was a pleasure to meet Congressman Boyle today,” Doherty said.

“He listened with compassion and interest to our testimony about Mary's death and was most concerned. He has great affection for Donegal - his father's homeland - and that is obvious not least because of the large picture of Glencolumbkille on his office wall.”

Spending all of last week in Washington D.C. meeting with politicians, Doherty also met with a series of senior politicians from Northern Ireland including Secretary of State Theresa Villiers, First Minister Arlene Foster, Deputy First Minister Martin McGuinness, and Nigel Dodds DUP MP for North Belfast.

They also met with former congressman and human rights lawyer Bruce Morrison and Fr. Sean McManus of the Irish National Caucus.

PSNI Chief Constable George Hamilton and chair of the Northern Ireland Policing Board Anne Connolly have since agreed to meet with Doherty in Belfast in the coming months after they were informed of the case, in particular of the allegations of Garda malpractice in the investigation.

"Having spent a number of days in Washington D.C. meeting politicians and others, I've have to say I have encountered more concern for my sister here than in the corridors of power in Ireland where Frances Fitzgerald and Micheál Martin both refuse to meet me,” Doherty stated.

“I hope Irish-American politicians can use their influence now and encourage the government to set up an independent inquiry into the allegations of corruption in the case and also to impress upon Garda Commissioner Noirin O'Sullivan that an arrest of Mary's killer is long overdue.

“I am asking him once again to return Mary's remains to me so that I can give her a proper burial, have a grave to visit, and try to achieve some sort of closure for myself."

The murder of Mary Boyle: Irish cold case team will pursue Ireland's oldest missing person case.Ann Doherty