On the day Rosemary Nelson was killed, her attackers visited her home not once, but twice. Police have built up a detailed picture of how the attack was carried out and while they privately concede that grey areas remain, this strange turn of events has been confirmed.
In the early hours of March 15 1999 the gang planted an under-car bomb below Mrs Nelson's silver BMW while it was parked outside her Lurgan home.
They must have expected her to leave for work early that morning, for it has now emerged that when she did not, two of the gang drove back to her home to find out why the booby-trap device had not exploded.
When they saw Mrs Nelson's car still parked outside her house they drove away and waited.
It was not uncommon for Mrs Nelson to phone ahead to the staff in her Lurgan solicitor's office, only to join them later.
She left for work at around 12.30pm.
The mother-of-three had driven only yards from her home when the device beneath her car exploded. She died a little over two hours later in hospital.
Only a few years before her death, Rosemary Nelson was unknown outside her home town.
She ran her own solicitor's office in Lurgan, Co Armagh, and gained a reputation as an effective lawyer.
But by the mid-1990s she had taken on three clients whose cases eventually brought the 40-year-old to wider attention.
Lurgan republican Colin Duffy was twice cleared of murder charges under her representation. In one case, the main prosecution witness was exposed as a loyalist paramilitary.
Mrs Nelson was also asked to represent the Garvaghy Road Residents Coalition and found herself drawn into the bitter Drumcree marching dispute.
She later represented the family of Portadown Catholic Robert Hamill, who was kicked to death by a loyalist mob while police were parked nearby.
As these cases raised Mrs Nelson's profile, she began to receive threats from loyalists. She also claimed that police officers interviewing some of her clients had issued threats against her.
Her case attracted the attention of international human rights groups and was raised at the United Nations.
The solicitor's death came despite calls for her protection and international demands for an independent inquiry.
The authorities resisted pressure for the RUC to be barred from the murder hunt. The inquiry team, led by a senior English officer, comprised a mix of RUC staff and police drawn from Britain.
Deputy chief constable of Norfolk Colin Port, who led the police team, stepped down as head of the investigation three months ago. A successor has yet to be appointed, but police insist that the murder hunt is continuing.
But after a four-year probe that has cost in excess of £7 million, it is unclear if police are any closer to catching Mrs Nelson's killers.
Investigators have stressed that they went to unprecedented lengths to gather evidence against suspects, but the killers have yet to be brought to justice and the concerns of security force collusion in the murder linger on.
Mrs Nelson was in Donegal on the weekend before her death, but her car was parked outside her home from the early evening of Sunday March 14.
She lived in a quiet residential area, not covered by CCTV.
It is now thought that two suspicious cars seen in the area around midnight are likely to have carried the gang that planted the bomb.
These cars have never been located.
The bomb would have been attached to Mrs Nelson's car in seconds.
It is now known that it contained 1lb of powergel explosives, with a triggering mechanism that included a mercury tilt-switch. Other such devices had fallen off the vehicles they were attached to, but the bomb which killed Mrs Nelson included a powerful magnet stolen from Harland and Wolff shipyard in Belfast.
The device was examined for features that might indicate the 'signature' of the bombmaker and similarities were found with two car bomb attacks launched by loyalists.
In December 1996 Belfast republican Eddie Copeland suffered leg and arm injuries but escaped with his life when loyalists planted a similar booby-trap beneath his car.
In October of the following year, it is thought that the bomb-maker increased the amount of explosives used in the device.
This was used to target Co Down man Glen Greer during a feud between the UVF and UFF. The Bangor man died as the explosion ripped through his car.
The Red Hand Defenders, who claimed responsibility for Mrs Nelson's murder, was seen as a flag of convenience used by a coalition of loyalists opposed to the peace process.
At the time, the sophistication of the device was thought to be beyond anything the grouping had access to. It was quickly established that the attack was carried out by members of the LVF, working with members of the larger loyalist paramilitary organisations.
The Irish News now understands that investigators have identified between eight and 10 suspects who they believe were involved in the bombing. These include three high profile loyalists who are known to the police and were highly active in the Portadown/Lurgan area around the time of Mrs Nelson's murder.
Former LVF leader Mark 'Swinger' Fulton is believed to have coordinated the attack on Mrs Nelson. He was in prison on the day of the murder, but he was granted parole in the days leading up to the killing and he is also thought to have contacted his accomplices from jail.
Fulton, a close associate of the LVF founder Billy Wright, was found dead in his cell in Maghaberry prison in June last year. The authorities have concluded it was suicide.
Police are also believed to have identified a loyalist in his mid-forties, who has been connected with both the UDA and UVF, as the man they suspect built the bomb, but they have been unable to gather evidence against him.
The list of suspects also includes two men with links to the security forces.
The first is in his early thirties and was a soldier in the RIR at the time of the killing, but left within two months of it.
The second is a Co Armagh-based loyalist who was identified in a court case, unrelated to the Nelson murder, as being a police informant.
The men's security links have fuelled the speculation of collusion in the killing, but it is understood that police have denied this is the case. They claim that the exact role of both men remains in doubt, while they portray the former soldier as a maverick who admired Billy Wright and was keen to help develop the capabilities of the LVF.
The remaining suspects are a mixture of well known loyalists and lesser known figures on the fringes of dissident loyalist activities.
Police say they went to great lengths to gather evidence on these suspects.
Individuals were targeted for surveillance and undercover operations, with the aim of securing information that might pave the way for convictions.
This work may have helped police jail some of the suspects for other illegal activity, but it failed to unearth sufficient evidence to support charges in relation to Mrs Nelson's murder.
During the course of the investigation, the Rosemary Nelson team made 30 arrests, carried out 69 house searches, took 4,864 statements and recorded over 11,000 investigative tasks carried out by officers. This resulted in 17 people being charged in connection with illegal activity including serious paramilitary related crimes. None of these charges, however, related to the murder of Rosemary Nelson.
From the outset of the investigation there were concerns over its ability to get to the bottom of the allegations of security force collusion in the killing.
At its height the Rosemary Nelson team included 150 police staff.
They continue to insist that no evidence has been found to support the fears of collusion.
At the time of Mrs Nelson's killing, concerns were expressed over reportedly high levels of security force activity near her home in the days leading up to the attack. One observer has questioned "the bombers surprising degree of self-confidence".
Mrs Nelson is known to have remarked upon the helicopter activity near her home on the night before her death in a telephone conversation with a close relative.
Police have claimed, however, that the activity levels were high for at least two weeks and say that it has now been accounted for.
While investigators studied the security force movements in detail it is believed this process was complicated by the fact that very little of the helicopter activity was actually recorded.
Despite police claims that they have found no evidence of collusion, close observers of the case have identified areas of concern, which they say remain.
The inquiry team was urged to question the police officers accused of threatening the defence solicitor. But police argued that earlier probes found insufficient evidence to bring charges against these officers and, in the absence of new evidence, they saw no grounds for questioning them again.
In the wake of the murder, two weeks passed before Colin Port was named as the outside officer who would take over the inquiry. The murder and collusion investigation was, therefore, under way before any outside scrutiny of its day-to-day activities began.
While there is no suggestion that this hampered the murder hunt, it has undermined the independence and transparency that Mr Port's arrival was intended to stamp on the investigation.
In addition, it has been claimed that a number of leaks to the media possibly alerted suspects.
Four years after the murder of Rosemary Nelson, her killers have yet to be prosecuted. But the history of the Troubles is dotted with similar human tragedies where the guilty have evaded arrest.
The unique element in Mrs Nelson's case is that a two-year campaign, which included concerns for her safety being raised by the international human rights community, failed to save her.
Four years after her murder, Rosemary Nelson's killers have yet to be brought to justice, while the allegations that she became a target for abuse by sections of the security forces, continue to fuel fears of collusion in her killing.
Observers argue that the Rosemary Nelson investigating team has made considerable progress in disrupting the operations of the LVF, but has so far failed in the job for which it was created.
