Fourteen people have been linked to "evidential activity" in the days leading up to and on the day of the Omagh bombing, the inquiry into the explosion has heard.
Paul Greaney KC outlined the "working hypothesis" of the inquiry when it resumed its latest phase on Monday.
In a statement to the inquiry, sitting at Bradford Court in Belfast, he named Seamus McKenna, Seamus Daly and Colm Murphy as among the 14.
Twenty-nine people, including a woman pregnant with twins, died in the bombing in the County Tyrone town on 15 August 1998 - the biggest single atrocity in the Troubles.
'Like a spider in web'
In 2009, a judge ruled that four men - Michael McKevitt, Liam Campbell, Colm Murphy and Seamus Daly were all liable for the Omagh bomb.
A fifth man, Seamus McKenna, was acquitted in the civil action and later died in a roofing accident in 2013.
On Monday, Greaney told the inquiry: "The evidence suggests Colm Murphy sat like a spider in the centre of the web of the plan to detonate a bomb in Omagh".
Referring to the civil case, Greaney said: "The fact Seamus McKenna was not found liable is not an outcome which binds this inquiry. Our working hypothesis is that, contrary to that finding, he played a key role".
The use of telecommunications is a key part of the evidence in front of the inquiry and some of the most frequently referred to mobile phones have been assigned colours for ease of following their links.
The inquiry heard how it was "likely" that the Vauxhall Cavalier car used in the bombing was "stolen to order" in the days before the bombing.
Evidence was outlined that on 14 August 1998, the day before the bombing, a "test run" of the journey to the bomb site was carried out in a Volkswagen Golf car.
The principal objective of this chapter of the inquiry is to understand how the bombing was carried out and by whom.
Among the witnesses this week will be a senior garda officer who is expected to provide initial evidence about the theft of the car used in the explosion.
It was stolen in Carrickmacross, County Monaghan two days before the explosion.
The inquiry was established to determine if the bombing could have been prevented by UK state authorities.
The third phase is expected to last about four weeks.
What was the Omagh bomb?
The Omagh bomb exploded on 15 August 1998, killing 29 people including a woman pregnant with twins.
It came less than three months after the people of Northern Ireland had voted yes to the Good Friday Agreement.
No-one has ever been convicted of the atrocity.
Who carried out the Omagh bombing?
Three days after the attack, the Real IRA released a statement claiming responsibility for the explosion.
It apologised to "civilian" victims and said its targets had been commercial.
No-one has been convicted of carrying out the murders by a criminal court.
In 2009, Michael McKevitt, Liam Campbell, Colm Murphy and Seamus Daly were all ordered to pay a total of £1.6m in damages to the relatives, but appeals against the ruling delayed the compensation process.