The inquiry into the Omagh bombing has heard from an academic expert on dissident republicanism.
Twenty-nine people, including a woman pregnant with twins, died in the Real IRA bombing in the County Tyrone town on 15 August 1998 - the biggest single atrocity in the Troubles.
It came less than three months after the people of Northern Ireland had voted yes to the Good Friday Agreement.
The inquiry, which opened last year with 14 days of testimony from bereaved families and survivors, was established to determine if the bombing could have been prevented by UK state authorities.
Dr John Morrison, associate professor in criminology at Maynooth University, gave evidence to the inquiry on Tuesday.
Morrison said he classified violent dissident republican groups, such as the Real IRA and the Continuity IRA, as groups which "espouse the continuation of what they refer to as the armed campaign or armed struggle".
This led to a split in the group leading to the formation of the Real IRA.
Morrison said "while the membership was small, they had significant experience, expertise, and access to weaponry within their membership to enable them to engage in extreme violence from the outset".
In a report provided to the inquiry, Morrison named Michael McKevitt as a quartermaster general of the Real IRA and said his aim was to "pursue a strategically timed campaign of bombing in Northern Ireland and Britain".
He said the Real IRA was most prominent in border counties, but also in Dublin and Cork.
When asked if Dundalk was a "home for and base" of the Real IRA, he agreed.
He said "it is clear that the Real IRA at the time of the Omagh bomb was a new group with a relatively small membership of up to 90 members, approximately a third of which would have been violently active".
The inquiry also heard that there was "some form of operational co-operation for the Omagh bombing between the Real IRA and the Continuity IRA".
Inquiry objectives
The principal objective of this chapter of the inquiry is to understand how the bombing was carried out and by whom.
Among the other witnesses this week will be a senior Garda officer who is expected to provide initial evidence about the theft of the car used.
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.
More than 200 people were injured in the blast.
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.