Malaysian Nasir Abbas was a senior leader with Jemaah Islamiyah and trained all the Bali bombers in weaponry and warfare at a mujahedeen camp in Afghanistan.
His sister was married to executed Bali bomber Mukhlas, brother of one of the other bombers Ali Imron, and he was once one of South East Asia’s most wanted Jihadis.
A two-part Dateline special brings three of the bereaved face-to-face with Abbas and Imron, as they try to understand what happened and why.
Abbas says he used to be a terrorist, but isn’t any longer after turning informer and giving evidence against friends and fellow extremists.
Now he works with the authorities on deradicalisation.
“Their sins weigh heavily on me. I have to set them on the right path,” he tells widows Nyoman Rencini and Ni Luh Erniati in part one of Dateline's Meet the Terrorists.
“I have to persuade others not to do this again. I bear this burden. I feel as though I’ve sinned too… today my jihad is against the terrorism action.”
He now attends support meetings run by Ni Luh, and also accompanies Australian Jan Laczynski as he lights memorial candles for those who died.

Nasir joins Jan Laczynski from Melbourne as he remembers those who died, including five of his friends. Source: SBS
“I want to meet all of the families of the Bali bomb victims,” he says. “What kind of response? I’m ready to face it."
In the second part of Dateline’s story, the three bereaved meet bomber Ali Imron: