There have been numerous expressions of outrage and sadness at the murder of Ms Rosemary Nelson, who has been a frequent visitor to the US to promote human rights in Northern Ireland.
The First Minister, Mr David Trimble, in whose constituency the killing took place, said he was "horrified" and extended sympathy to her family.
Speaking at the US Department of Commerce where he was attending an announcement about new jobs in Northern Ireland, Mr Trimble said if the murder was committed by those who wanted to endanger the peace process, "that underlines the need to ensure they will not succeed".
Only last September Mrs Nelson spoke about death threats against her when she was testifying to the human rights sub-committee on Capitol Hill.
The chairman of the international relations committee, Mr Ben Gilman, asked her if she had requested security as a result of the threats.
She replied that she had not made "any specific requests for security, but the RUC was notified about these threats. They have continued to be notified about them."
She agreed with Mr Gilman that "the government does have responsibility" but went on to say that "the procedure there is, if you request security from the RUC, your house or your premises are assessed by the RUC for these security installations. And I wouldn't have any great faith in the RUC coming in to assess that."
The Deputy First Minister Mr Seamus Mallon, who is also in Washington, said the killing "shows in a murderous and grotesque way how important the peace process is and that nothing must be allowed to endanger the cause of peace".
Sinn Fein president Mr Gerry Adams, who is travelling in the US, said he was shocked at the murder. "The attack on Rosemary Nelson is an attack on the Good Friday agreement which proclaims the right of citizens to live free from sectarian abuse."
Mr Adams said that "Like Pat Finucane before her, Rosemary Nelson has fought against state injustice and in particular the excess of the state police - the RUC. For this she has been threatened many times."
Mr Adams said that Mr Trimble, who has "refused to meet and talk to the residents of that small besieged Catholic community", must now "change his stance after today's murder".
Congressman Chris Smith called the murder a "gross atrocity" and demanded that the British government fully investigate it.
Mr Smith, who is chairman of the human rights sub-committee to which Mrs Nelson testified last year, said: "While no one knows who committed this cowardly act, if the Blair government is serious about ending the intimidation of defence attorneys in Northern Ireland, they must vigorously investigate every possibility, including collusion."
He said that "It is obvious that the RUC cannot be entrusted with this investigation. The circumstances of her death, her fear of the RUC, and her own forecast that something horrible may happen to her makes it absolutely necessary that an investigative body other than the RUC and security forces investigate her murder."