The US House of Representatives has passed a resolution calling on the British Government to set up a fully independent inquiry into the murder of Pat Finucane.
The move follows lobbying from the family of the Belfast solicitor, who was shot dead by loyalist paramilitaries in 1989.
There have long been allegations that the British security services helped the men who carried out the shooting.
The British Government has set up an inquiry, but the family are refusing to co-operate as certain evidence can still be kept secret.
They want a fully independent inquiry where all evidence can be assessed and witnesses compelled to testify.
On a vote of 364-34 with 25 members voting "present," the House accepted a resolution that demanded "the establishment of a full, independent and public judicial inquiry into the murder of Patrick Finucane."
It also urged the British government to scrap the 2005 Inquiries Act that allows it "to block scrutiny of state actions," under which a previous investigation into Finucane's death was carried out.
Republican U.S. Representative Chris Smith said the British government should "live up to its commitment as part of the Northern Ireland peace process to implement a public, independent, judicial inquiry into the murder of courageous human rights attorney and activist."
"The questions of police collusion surrounding his murder need to be answered," he said.
Democratic Representative Tom Lantos, chairman of the House foreign affairs committee, said: "The time to bring justice and put an end to this tragic matter is long past due."