A public inquiry into solicitor Rosemary Nelson's murder will hear from more than 100 witnesses after it begins this week.
The hearing into one of the most controversial killings during three decades of violence in Northern Ireland is expected to last at least a year.
Retired High Court judge Sir Michael Morland will chair a three member panel examining claims that the security forces plotted with loyalist terrorists who murdered the lawyer in a car bomb attack at her home in Lurgan, Co Armagh in March 1999.
He said: "The Rosemary Nelson Inquiry seeks to find out the truth.
"We are here to work with fairness, thoroughness and impartiality to establish the facts and to make recommendations."
The British government agreed to set up an inquiry into Mrs Nelson's death based on the recommendations of Canadian Judge Peter Cory, who found enough evidence of possible collusion to warrant further investigation.
He also called for tribunals into the assassination of Belfast solicitor Pat Finucane, the jailhouse shooting of loyalist paramilitary chief Billy Wright, and the fatal mob attack on Catholic man Robert Hamill.
In a fifth case, the Government has agreed to hold an inquiry into the IRA murders of two senior RUC officers Bob Buchanan and Harry Breen.
When the Nelson hearing begins on Tuesday, Sir Michael and his colleagues - ex-Chief Constable of South Wales Sir Anthony Burden and Dame Valerie Strachan, former chair of the Board of Customs and Excise will study allegations that police ignored death threats against her.
Mrs Nelson became a hate figure among some loyalists after she represented nationalist residents during the flashpoint Drumcree marching dispute.
Northern Ireland Secretary Paul Murphy has extended the inquiry's terms of reference at the panel's request.
PA