Ali Imron was giving evidence on Monday at the trial of Abdul Ghoni, who could face a firing squad if found guilty of helping to plan the attacks, assemble the bombs and of possessing explosives.
Imron had been jailed for life for his role in the nightclub bombings, which killed 202 people in the holiday on 12 October last year.
Three other key suspects, including two of his brothers, had been sentenced to death, but Imron received a lighter sentence after expressing remorse.
Police said the Jemaah Islamiyah (JI) carried out the attacks to avenge injustices against Muslims worldwide.
However, Imron, 33, revised statements he made in earlier trials.
Ali Imron expressed remorse for
He said he had earlier mistakenly stated the bombers were allotted their tasks during a meeting at the home of a man called Hernianto at Solo in Central Java.
"I remembered that there was a meeting and during the re-enactment at Hernianto's place, I felt it was the place. But after I talked to Idris (another suspect) I remembered that it was at one of the rented houses of Dulmatin, not at Hernianto's," Imron told the court.
Idris, alias Jhony Hendrawan, has not yet been tried while Dulmatin is still on the run. Hernianto has been jailed for 12 years as an accomplice.
Imron said the meeting at Hernianto's was a social gathering and nothing in particular was discussed.
He said that during the meeting at Dulmatin's house, Ghoni was tasked with mixing the ingredients for the bomb.
But when it was actually made, Ghoni did not take part in mixing the ingredients, Imron alleged. "The one who assembled the bomb was Dulmatin."
Imron said he first met Ghoni in Afghanistan in 1991. They met again in Solo in 2002 and twice in Bali in October before the bombings.
Prosecutors said Ghoni - alias Umar, alias Wayan - helped mix the chemicals on 1 October after he had crushed the ingredients a month earlier.
They said he personally delivered four boxes of explosive material to Bali and, on the orders of Imam Samudra, delivered $1100 to Amrozi in East Java on 4 October.
The Bali bombings killed 202
Samudra and Amrozi, along with Mukhlas, have been sentenced to death.
Prosecutors have said the largest bomb, packed into a van, consisted of 12 filing cabinets filled with 900 kg of explosive materials including aluminium powder and sulphur.
It devastated the Sari Club and caused most of the casualties.
Imron has admitted driving the van near to the club before another man took over, and that he taught a bomber in Paddy's Pub how to detonate an explosives-stuffed vest.
Ghoni's trial resumes on 8 December.