BRAINTREE -- To some, Jack Sheehy's great-great grandfather was a criminal but to others, including Sheehy, he was a hero.

Sheehy, of Tewksbury, is a descendant of Denis Cashman, an Irish freedom fighter and business manager of The Pilot whose tumultuous life took him from Dungarvan, County Waterford to an Australian prison to an unmarked grave in Chestnut Hill's Holyhood Cemetery.

"It's pretty fascinating, the various things he did," Sheehy said.

Cashman will receive a gravestone from the National Graves Association of Ireland, an organization dedicated to maintaining the graves of Irish patriots. The new stone, whose design is such a closely guarded secret that not even Sheehy knows what it looks like, will be unveiled with a ceremony at Holyhood Cemetery on Sept. 13. Over 20 of Sheehy's relatives are coming across the country for the occasion.

"It's nice to have closure there," he said. "My family has some interest in history in general, and to have some of our own direct ancestors involved in a story like this is a really fascinating thing. It makes you feel proud that there is enough interest for people over in Ireland that they would go through this whole process for him."

Cashman was a member of the Fenian Brotherhood, a group of secret societies in Ireland and the U.S., which fought British rule. The term Fenian came from the Fianna, legendary warriors of Irish folklore.

On Jan. 12, 1867, the same day his third child was born, Cashman was arrested. His alleged crime was manufacturing rifle cartridges and providing weapons to the Fenians. The 25-year-old was subsequently found guilty of treason against the British Crown. Due to his youth, the court offered a plea deal that would reduce his sentence. He refused.

"If I had my life to live over I would do it all again," he reportedly said. "I am willing to die for Ireland."

He was taken to Australia aboard the Hougoumont, the last ship that transported prisoners to Britain's Australian penal colonies. He and other Fenians on board founded the ship's newspaper, The Wild Goose. Cashman wrote a diary detailing his experiences on the Hougoumont. The original handwritten journal made its way to his granddaughter, Sheehy's grandmother. Her possession of the diary was a secret she revealed only to a precious few. After her death, Sheehy's uncle received the diary and donated it to East Carolina University, where it was researched and published. That was when most of the Sheehys found out about their ancestor.

"He was someone who held very strongly to his ideas," Sheehy said, adding, "You do have to be impressed with his determination to follow his beliefs, even in peril to himself."

Cashman was pardoned in 1869 and sailed to San Francisco, then went to Boston to reunite with his family. He worked as business manager for The Pilot alongside editor John Boyle O'Reilly, himself a Fenian who had been imprisoned in Australia before escaping to the U.S. The two men helped plan the Catalpa Rescue, an 1876 plot in which six Fenians escaped from an Australian prison with the help of a New Bedford merchant ship purchased by O'Reilly and Cashman's co-conspirators. Cashman was a pallbearer at O'Reilly's funeral.

Along with being business manager, Cashman wrote articles for The Pilot and was an outspoken voice for Irish independence. After leaving The Pilot, he worked as superintendent of Boston's Waste Water Department and as a salesman for Donahoe's, a Catholic magazine. He died in 1897.

Sheehy family lore held that Cashman was buried in Holyhood Cemetery, perhaps next to O'Reilly, but the exact location remained unknown.

Sheehy's aunt Mary and her daughter Susan O'Sullivan "did most of the legwork" to give Cashman his stone, he said. The NGAI researched the matter and pinpointed the exact location Cashman, his wife Catherine, and his five children were buried (the location of his son William Patrick's grave is still unknown). A fundraiser by the NGAI raised 4,822 euros ($5,611) for the stone. It will join two other markers of the spot where Cashman is buried: a U.S. flag, and an Irish one.