British police have found fresh forensic evidence in the murder of an Irish farmer by the IRA in 1991, a discovery that could identify suspects and also undermine the government’s plan to end prosecutions for killings during the Troubles. Detectives from Operation Kenova, a wide-ranging investigation into unsolved murders in Northern Ireland, said on Monday they had found DNA evidence in relation to the abduction and shooting of Tom Oliver. “We have made good progress with the investigation including recovering new DNA evidence from forensic testing of items recovered during the initial investigation. But we still need more information to bring those responsible to justice,” said Jon Boutcher, the former chief constable of Bedfordshire who heads Operation Kenova. The renewed possibility of catching the killers overlaps with Boris Johnson’s plan, announced last week, to grant what critics call a de facto amnesty to former security force personnel and paramilitaries accused of murders during the Troubles. The proposal envisages a statute of limitations on prosecutions and an end to inquests and civil cases. Victims groups, all Northern Irish political parties and the Irish government oppose the plan, which is seen as an attempt to shield former soldiers from prosecution for killings dating from the early years of the Troubles. A small group of relatives is to protest outside Downing Street on Tuesday. It will include Julie Hambleton, whose sister was killed in the IRA’s 1974 Birmingham pub bombings, and Joe Campbell, whose father, a member of the Royal Ulster Constabulary, was murdered by the UVF in 1977. The investigation into the murder of Oliver in July 1991 could prove awkward for the government, which maintains that the criminal justice system is unable to solve cold cases or provide answers to bereaved families. The 43-year-old father of seven owned a farm in County Louth, just inside the border with the Republic of Ireland. He was abducted near his home on 19 July 1991. The body was found dumped the next day near the village of Belleeks in County Armagh, Northern Ireland. Oliver had been shot six times. The body bore injuries consistent with torture. The IRA suspected Oliver of being a Garda informer, which the family vehemently denied. Even by the brutal standards of the Troubles it was a shocking murder, which embarrassed Sinn Féin, even more so when it was later alleged that Oliver was killed to protect the identity of a British agent within the IRA known as Stakeknife. Operation Kenova was originally set up to investigate Stakeknife. Boutcher said his team had “an understanding of the people” involved in the crime. Addressing journalists on the 30th anniversary of Oliver’s abduction, from a field where Oliver’s car was found, the former chief constable said the investigation had taken a significant number of new statements and was following lines of inquiry on both sides of the border and in Australia. He appealed for information about a grey Ford Orion car detectives believe was used to transport Oliver’s body. “And a female called the information line for the police and explained what she saw. We desperately want that lady to contact us,” said Boutcher. He thanked Irish police for cooperation but confirmed that some former gardaí had declined to be interviewed. “We don’t necessarily take ‘no’ for an answer.” In a statement the Oliver family said they hoped the DNA evidence would help solve the case. “After 30 years, there is now light at the end of a very dark tunnel.”