The inquiry has examined claims that police made threats against the lawyer, plus allegations of security force collusion in her killing.
The 40-year-old mother-of-three died when a bomb exploded underneath her BMW car as she left her home in Lurgan, Co Armagh, on March 15, 1999.
Her legal practice dealt with mainly routine cases but she had risen to prominence and earned dangerous enemies after taking on a number of high profile clients, including suspected republicans.
Mrs Nelson’s murder came within a year of the signing of the Good Friday Agreement, but it was an unstable period. As decades of violence gave-way to a new era of political negotiation, warring ideologies feared losing advantage.
The solicitor found herself representing clients whose cases placed her at the centre of some of the most controversial episodes of the period.
They included Lurgan republican Colin Duffy, who in the 1990s was acquitted of the murder of a former soldier, while claims he killed two police officers also collapsed. He is currently charged over the murder of two soldiers shot dead by dissident republicans in Antrim in 2009.
Other clients include the nationalist Garvaghy Road residents’ group as it opposed Orange Order parades in the bitter Drumcree stand-off in Portadown.
As tensions grew, Mrs Nelson claimed that Royal Ulster Constabulary (RUC) officers questioning her clients had made death threats against her. That alleged misconduct matched that reported by Belfast solicitor Pat Finucane before he was shot dead by loyalists in 1989.
Mrs Nelson’s murder was claimed by the loyalist Red Hand Defenders, but her death sparked immediate claims of a possible security force link. In 2001 a review of the case by retired Canadian judge Peter Cory found sufficient “evidence of collusion by government agencies” to warrant a public inquiry.