Murder mystery: Dr Paddy Muldoon, who was gunned down in Mohill, Co Leitrim, just weeks after a baby was abandoned near the Black Church in Dublin

In February 1923, as the Irish civil war was drawing to a close, a Catholic priest was arrested with his housekeeper on a charge of abandoning a baby on the doorstep of a house in Dublin's north inner city.

Three local women had noticed the curate, Fr Edward Ryans, and the teenage girl acting suspiciously before they left the infant and a package wrapped in brown paper near the Black Church in Broadstone.

The vigilant women apprehended the couple from Leitrim as they tried to hurry away, before reporting them to police.

A month later, Paddy Muldoon, a young doctor from the same area in Leitrim, was walking late at night down the street in Mohill with a friend, Edward Geelan, when suddenly three men appeared in trenchcoats.

Muldoon and his friend were just saying goodbye near the bridge, when one of the men opened fire at Dr Muldoon.

The doctor pleaded with the gang "Don't shoot", but they fired at him three times, and he fell to the ground.

The young doctor left behind a widow, Rita, and four children. Although there were clear suspicions and there has been plenty of speculation about the killing in Mohill until this day, nobody was ever prosecuted.

Were these two incidents - the abandonment of a baby girl and the subsequent murder of Dr Muldoon - linked?

Tim Desmond has sought to unravel the mystery of why the baby was abandoned and who organised the killing of the young doctor in a documentary that will be broadcast on RTE Radio 1 today.

He has sifted through evidence - including intelligence files, military correspondence and inquest reports - and he has talked to members of the Muldoon family and local historians.

He suggests that the priest who abandoned the baby was implicated in the killing of the doctor and the murder went unpunished because there was a cover-up - involving the Catholic Church, Free State authorities and the anti-treaty IRA.

Perhaps, some of those in authority were ready to let a murderer go free to avoid the scandal of a priest having sex with his housekeeper?

The 19-year-old girl at the centre of the case was working as a housekeeper for Fr Ryans when she became pregnant. Fr Ryans later gave a number of explanations about how the young woman became pregnant.

In one of his accounts, he said the father of the baby was a "friend of his family", who used to visit him in his house. As a result of the family link, he said he was anxious to have the matter "cloaked up".

But there was a widespread belief locally that the priest was the father of the child.

Fr Ryans sent the girl to Dublin for the last three months of her pregnancy, paying for her upkeep.

Giving a false name, 'Kate Brown', she gave birth to a girl in Holles Street Hospital. The baby was named on the birth certificate as Rose Brown - and there was no mention on the document of the father.

The mother and Fr Ryans dropped the baby on the doorstep in Broadstone two weeks after she was born.

Then, in the following month, the murder of Dr Muldoon happened. In the days after the shooting, Fr Ryans was immediately linked to the killing.

There were rumours of a connection to the events at the Black Church in Dublin a month earlier, and speculation that an IRA gang had been recruited to carry out the murder.

Fr Ryans was a significant figure in local republican circles and took the anti-treaty side in the civil war.

A statement from the anti-treaty IRA after the murder took responsibility for the killing while at the same time seeking to quell the speculation.

Issued by the publicity department of the Republican Party, the statement said: "It is being stated that a civilian was responsible for the death of Dr Muldoon, Mohill, Co Leitrim. This is entirely untrue."

The IRA claimed that volunteers had mistaken Dr Muldoon and his friend for Free State soldiers 'in mufti' and said that the pair had refused to halt when approached. The statement described the killing as an "unavoidable accident".

The explanation given by the IRA is seen as implausible, and is contradicted by evidence given at the doctor's inquest.

The widow, Rita Muldoon, wrote to newspapers, denying the IRA's claims.

Historian Cormac O'Suilleabhain, who is interviewed in the documentary, says: "It's easily the most intriguing and controversial killing of the time.

"A 32-year-old doctor married with three kids (the fourth child was on the way). He was quite well got, a well-respected man. It was obvious there was something underlying, something else in the background that caused it."

Having researched the events surrounding the murder for two years, programme maker Tim Desmond says: "We can't be 100% sure why the doctor was shot.

However, the evidence suggests that the doctor was killed because he had informed the Bishop of Ardagh and Clonmacnoise Joseph Hoare that the priest was the father of the child.

"The doctor knew that the priest was the father, because the girl had gone to him for assistance during the pregnancy. And he was willing to give evidence at the trial for the abandonment of the child."

Desmond says the evidence indicates that the priest ordered, or persuaded, a local IRA gang to carry out the murder.

The priest's first problem that spring was to deal with the charge of abandoning the baby, with three witnesses testifying against him.

According to Desmond, the priest was tried three times and, in all three cases, the jury could not agree on a verdict.

"The prosecution appears to have dropped the charges and there was no further trial," says Desmond. For much of this time, the priest was held in custody in Mountjoy Jail, but he was released in late 1923.

Meanwhile, there was an investigation into the murder of the doctor and Fr Ryans was prime suspect. General Sean Mac Eoin of the Free State national army was heavily involved in dealing with the case.

"An initial army report by General Mac Eoin puts Fr Ryans right in the frame," Desmond says.

The criminal investigations department (CID) came to Mohill to look into the case and took statements. According to Desmond, they also established that the priest was the chief suspect.

But no charges were brought against Fr Ryans for the murder. "There was a feeling that this individual had done bad things, but rather than prosecute him, there was an agreement that he would go away," Desmond says.

"The priest agreed with the Bishop's suggestion that he should go away. That was his punishment."

Fr Ryans sailed to America two years after the murder, spending time in Florida and Nevada, before moving to Morecambe in Lancashire. He was confronted at least once by a member of the Muldoon family, but vehemently denied the killing until his dying day.

The baby at the centre of the abandonment case died of gastritis in a 'mother-and-baby' home just a few months after she was born and little is known about what happened to her mother.

An Unholy Trinity, RTE Radio 1, today, 1pm

Belfast Telegraph