A mass grave containing the remains of babies and young children has been discovered at a former Catholic mother and baby home in Ireland, government-appointed investigators announced Friday in a finding that offered the first conclusive proof following a historian's efforts to trace the fates of nearly 800 children who perished there.

The judge-led Mother and Baby Homes Commission said excavations since November at the site of the former Bon Secours Mother and Baby Home in Tuam, County Galway, had found an underground structure divided into 20 chambers containing "significant quantities of human remains."

The commission said DNA analysis of selected remains confirmed the ages of the dead ranged from 35 weeks to three years old.

They were buried chiefly in the 1950s, when the overcrowded facility was one of more than a dozen in Ireland offering shelter to orphans, unwed mothers and their children. The Tuam home closed in 1961.

Members of the public at the site of a mass grave for children who died in the Tuam mother and baby home, in Tuam, County Galway. Forensics experts say they have found a mass grave for young children at a former Catholic orphanage in Ireland where suspicions of unrecorded, unmarked burials have lingered for decades. (Niall Carson/Associated Press)

Friday's findings provided the first proof after decades of suspicions that the vast majority of children who died at the home had been interred on the site in unmarked graves.

That was a common, but ill-documented practice at such Catholic-run facilities amid high child mortality rates in early 20th century Ireland.

The government in 2014 formed the investigation after a local Tuam historian, Catherine Corless, tracked down death certificates for nearly 800 children who had died as residents of the facility — but could find a burial record for only one child.

"Everything pointed to this area being a mass grave," said Corless, who recalled how local boys playing in the field had reported seeing a pile of bones in a hidden underground chamber there in the mid-1970s.

Dublin Archbishop Diarmuid Martin attends a press conference at the Vatican in May, 2012. He said Ireland’s government should establish a fact-finding probe into the church’s mistreatment and burial of babies that died in nun-operated homes for unmarried mothers. (Andrew Medichini/Associated Press)

The government's commissioner for children, Katherine Zappone, said Friday's findings were "sad and disturbing." She pledged that the children's relatives would be consulted on providing proper burials and other memorials.

"We will honour their memory and make sure that we take the right actions now to treat their remains appropriately," Zappone said.

The report found that the dead children may have been placed in underground chambers originally used to hold sewage. Corless said she found records stating that the sewage systems were used until 1937, when the home was connected to a modern water supply.

[It's] the usual maddening nonsense. They must apologize and take responsibility for what happened there. - Catherine Corless, historian

A decommissioned septic tank had been "filled with rubble and debris and then covered with top soil" and did not appear to contain remains, the report said. But excavators found children's remains inside a neighbouring connected structure that may have been used to contain sewage or waste water.

The commission's finding that most of the remains date to the 1950s corroborates Corless' collection of death certificates. It also dispels a popular argument that bones seen at the site might predate the home's opening, when the building was a workhouse for the adult poor, or even be from people who died in the mid-19th century Great Famine.

In 2012, Dublin Archbishop Diarmuid Martin said Ireland's government should establish a fact-finding probe into the church's mistreatment and burial of babies that died in nun-operated homes for unmarried mothers.

Labour Party lawmaker Joan Burton said the dead may have been interred "without normal funeral rites, and maybe even without their wider families having been made aware." She called on the Catholic Church to provide more assistance to investigators.

Pledge to co-operate

The investigators, who are examining the treatment of children at a long-closed network of 14 Mother and Baby Homes, said they still were trying to identify "who was responsible for the disposal of human remains in this way."

The Bon Secours Sisters order of nuns, which ran the home until it closed, said in a statement that all its records, including of potential burials, had been handed to state authorities in 1961. It pledged to co-operate with the continuing investigation.

Corless criticized the Bon Secours response as "the usual maddening nonsense. They must apologize and take responsibility for what happened there."

She called on the nuns to promise explicitly to help the state organize proper marked burial places for every dead child once each set of remains could be identified.

"That's the least that can be done for them at this late stage," she said.