The 31 handwritten volumes of embittered 17th-century testimony have been alternately hailed as the world's first war crimes investigation or damned as a prototype dodgy dossier packed with black political propaganda.

Witness statements taken after the Irish rebellion and massacres of 1641 – that provided Oliver Cromwell with justification for his infamous slaughter of the defeated garrisons at Drogheda and Wexford – are being put online and will for the first time be cross-checked, where possible, for accuracy and exaggeration.

In what has been dubbed as the ultimate in cold case reviews, historians, linguists, software specialists and the public are being invited to trawl through newly transcribed versions of the original documents held in Trinity College, Dublin.

The 350-year-old writing is barely legible, the spelling across 19,000 pages of text erratic. The events they chronicle, however, poisoned Anglo-Irish relations for centuries, focusing attention on atrocities inflicted predominantly by dispossessed Irish Catholic rebels on Anglo-Scottish, Protestant settlers. The barbarities are still emblazoned on Orange Order banners and loyalist murals in Northern Ireland.

As late as the 1930s the Irish government intervened to prevent publication of historical research about the accounts of arson, communal murders, mass drownings, lynchings and robberies because it was deemed to contain such incendiary allegations.

Academics from Trinity College, Aberdeen and Cambridge Universities are now co-operating on a series of research projects that could not only help bring resolution to ancient quarrels but will open up a treasure house of genealogical, linguistic and census information.

Professor Jane Ohlmeyer, one of the principal investigators at Trinity, believes that new language analysis methods will allow the documents to be explored "in a way we couldn't have done 10 or 15 years ago during the Troubles".

The rebellion, which broke out in October 1641, was a significant moment in the formation of identity in Ireland, she told the Guardian. Estimates of the numbers killed vary from 4,000 to up to 200,000. It began in Ulster but spread across the country.

The depositions were ordered by government commissioners, many of the Church of Ireland clergymen, who recorded the victims' testimonies.

"They did it in the hope of obtaining evidence against the rebels and also as a crude form of insurance claim against lost property," Ohlmeyer said. Cromwell's commissioners were still taking evidence in the 1650s and the records form an extraordinarily detailed portrait of contemporary life, occupations and possessions in every Irish county.

The volumes were eventually donated to Trinity College in 1741, where they languished, rarely seen.

"In the 1930s a group of Irish scholars tried to publish them," Ohlmeyer said. "But the Irish government blocked them because it was too contentious.

"There are about 4,000 claims altogether. Nine times out of 10 they are not far off the mark because we have other sources we can check from the period. Now we can systematically analyse how accurate they were.

"There were clearly some atrocities such as the drowning of Protestants at Portadown where around 100 people lost their lives. That year was on record as one of the coldest winters and people died of starvation and cold.

"I was most moved by the account of one man who escaped to Dublin where he heard that his wife and children had been killed. He was reported to have died of grief. There's a lot of evidence from women, especially widows.

"The bloodletting was on both sides but Oliver Cromwell used this as justification for his [massacres at] Drogheda and Wexford. There were also a series of war crimes tribunals held by Cromwell in the 1650s."

The multi-disciplinary project has been funded by both Irish and British research councils. Students of the Holocaust and more recent genocides – such as Rwanda and the Balkans – as well as groups supporting peace and reconciliation in Northern Ireland have been among early users of the resources. It is hoped to have all the documents available online by the end of this year.

Another lead researcher, Barbara Fennell, a senior lecturer in language and linguistics at the University of Aberdeen, said: "These depositions tell us a lot about what English was like at the time.

"We hope to be able to synthesise some of the voices and make recordings of what they would have sounded like. They will be real echoes of the past.

"We know that different commissioners had different manners of speaking and writing. The language analysis software should be able to match up styles of speaking and writing ... so it may give us insights into any bias of evidence being introduced by a third party's influence. The historians say that Cromwell exaggerated the accounts to justify his actions. Is there any evidence of that as it was being written down?

"These collections are unique in early modern times. It is like doing a cold case review in the sense that we are using modern technological advances to provide insights into old evidence."

One of the 1641 depositions



Phillip Taylor late of the Portadowne in the County of Armagh husbandman ag sworne saith That about the xvj xxiiijth of October Last he this deponent was taken prisoner at Portadowne aforesaid by Toole mc Cann of now of Portadowne gent a notorious rebell and comander of a great number of rebells together with those Rebells his souldiers to the number of 100 persons or thereaboutes Att which tyme the Rebells first tooke the Castle and victualled the same, Then they assaulted and pillaged the towne & burned all the howses on the further side of the water And then the said Rebells drowned a great number of English protestants of men women and children in this deponents sight, some with their hands tyed on their backs And saith that the number of them that were soe then drowned amounted as this deponent was credibly tould and beleveth, to the number of 196 persons: And the same Rebells then alsoe threatened to shoote to death one Mr Tiffin a zealous protestant minister there & discharged a peece at him accordingly but as it pleasid god they mist him and at length he escaped from them: And further saith that the said Rebells kept this deponent in prison at portadowne aforesaid for the space of seven weekes and sett a horse Lock vpon his legg: but at length he gott a passe from the said Toole mc Cann & soe gotte away from them But whilest he stayd there many poore protestants were by the Rebells murthered in seuerall placs in about Loughgall aforesaid And they alsoe in that tyme stript of his clothes one Mr Jones a minister at Segoe nere Portadowne aforesaid: whoe afterwards escaped from them to the towne of Lisnegarvy: And the deponent hath credibly heard that one Mr ffullerton a minister & another in his company were alsoe murthered by the Rebells before the drowning of the protestants aforesaid And that the rebels signum dicti Phillippi Taylor [mark]