Almost three decades after British paratroopers opened fire on civil rights protesters in Derry, new forensic science evidence confirms that the demonstrators were unarmed.

The evidence was uncovered as part of an inquiry lead by the English judge Lord Saville, which was set up by British Prime Minister Tony Blair in 1998, after a long-running campaign by the families of the dead for the case to be re-examined.

Reports of the new evidence were given to lawyers for the families, who then released the contents to a news conference in Derry on Thursday.

Independent experts appointed by the Saville Inquiry described the evidence presented to an initial inquiry in 1972 under Lord Widgery as “worthless”. A second report indicates that one of the victims, Jim Wray, 22, was lying on the ground when he was shot twice. The report suggests that the bullets hit from a metre away, a conclusion that his lawyer said merited a murder prosecution.

Another victim, Barney McGuigan, a 41-year-old father of six, was shot in the head with a “dumdum” bullet. These fragment on impact and are illegal under the Geneva Convention.

Lawyers acting for the relatives of victims of what has become known as “Bloody Sunday” said the new reports were a damning indictment of the inquiry by Lord Widgery, which had exonerated the soldiers who claimed that they had been fired upon by protesters, thus justifying their response.

Dr John Martin, a Northern Ireland forensic scientist, carried out the original tests on victims in 1972. He found lead deposits on their hands and said this meant they had either fired a weapon, handled one recently fired, or been close to someone firing a gun. Martin now says that developments in testing show the same findings could be explained by contamination, including emissions from car exhausts. He says: “I now believe that where a test proved positive... this could have resulted... from contamination from other sources such as motor exhausts, which at that time were not fully evident.”

Solicitor Paddy MacDermott stressed that the reports totally discredited the original forensic evidence. It was not a case of developments within forensic science but that: “The important things is that this report could have been written in 1972. It is not a document that could only have been written because of scientific advances... It states that none of the deceased was proven to have used firearms, therefore this report effectively wipes out one of the main planks of the Widgery conclusions and effectively renders null and void the decision of the Widgery inquiry.”

The Widgery inquiry was broadly regarded as a political cover-up. The events in Derry on January 30, 1972 were to have a lasting effect upon the political situation in Ireland, and are seen as a turning point in the development of the so-called “Troubles”.

Thirteen unarmed civilians, all Catholics, were killed as British soldiers opened fire on a peaceful demonstration to demand an end to internment without trial. A fourteenth died later in hospital. Bloody Sunday marked a tragic and lasting refutation of the claims, made three years earlier, that the troops sent to Northern Ireland by the British Labour government were there to protect the Catholic population. Under these conditions, it was essential that Widgery exonerate the army.

Against damning eyewitness accounts by those present at the demonstration, Widgery concluded that “at one end of the scale, some soldiers showed a high degree of responsibility; at the other end ... firing bordered on recklessness”.

At the inquest into the Bloody Sunday dead, Derry coroner, Major Hubert O'Neill said, “the Army ran amok”. He described the incident as “sheer unadulterated murder”.

The British government later made out of court settlements with some of the bereaved families in order to prevent the prosecution of those responsible. The attitude of the British state towards the victims is revealed in a fifteen minute taped conversation between then Prime Minister Edward Heath and Irish Prime Minister Jack Lynch shortly after the massacre. Heath makes no expression of personal regret and demands that those who organised the march be condemned. The tape has been given to the Saville inquiry for consideration in its findings, which are to be presented in March next year.