Mr. Joyce was from a tight-knit community, and he was related to the five people who were killed in August 1882. In total, 10 men were arrested in connection with the murders, two of whom testified against the others. Five pleaded guilty and were sentenced to prison. The remaining three, including Mr. Joyce, were tried, convicted and hanged.

The victims — a married couple, Bridget and John Joyce; two of their children, Margaret and Michael; and John’s mother, Margaret — were found in their home in Maamtrasna, a remote community at the border of Mayo and Galway counties. Reports from the time — some of which included cruel descriptions of the Irish-speaking residents of that rural area — suggested that a firearm and some bludgeoning were involved.

Mr. Joyce and two others convicted of participation in the murder were hanged on a cold December morning in Galway. The New York Times reported that Mr. Joyce protested his innocence so persistently that he appeared to have prolonged his own execution:

Before the drop fell Myles Joyce spoke in Irish, as follows: “I am going before God. I was not there at all and had not hand or part in it. Lord, forgive them that swore against me.” He continued to reiterate his innocence to the end. The drop fell at 8:25 o’clock simultaneously for all three of the men. Myles Joyce alone struggled slightly, there being some hitch with the rope. His dying speech was delivered with much vehemence. He was still speaking when the drop fell.

A doctor who examined the bodies said Mr. Joyce struggled for minutes as the rope strangled him to death.

It was shown that after the rope had been adjusted around his neck he turned and addressed the reporters, thus disarranging the rope. The jury severely censured Marwood, the hangman, for his carelessness.

Ireland was not yet independent from Britain — that would not happen until 1921 — and the murders took place at a time of simmering conflicts over land rights and independence.

That made people wonder whether the murders were connected to the unrest, ultimately raising the profile of the case, Mr. Ó Cuirreáin said. Instead of being tried in nearby Galway, Mr. Joyce was taken all the way across the island, to Dublin, for his trial. English was the language of the court.

Professional Irish translators would have been easier to find in Galway, but in Dublin, a police officer was called upon to serve as a translator, Dr. Howlin’s research showed. But he mostly translated Irish into English and not the other way around, effectively leaving Mr. Joyce in the dark. The trial was also compromised by intense media interest, procedural problems, a lack of input from key witnesses and testimonial inconsistencies.

“The other two men convicted alongside him swore that he was innocent, and the approvers who had given evidence against him retracted their statements following his death,” Dr. Howlin said in her paper. Two years after the trial, The Times reported that one informer said he had been asked to lie by a crown solicitor. Mr. Ó Cuirreáin also found that a lord lieutenant of Ireland, Earl John Spencer, seemed to have been involved in bribing witnesses.

“It sounds like fiction because of the twists and turns,” Mr. Ó Cuirreáin said. “But unfortunately it was true, and innocent people were condemned to death.”