A former lawyer for Myuran Sukumaran and Andrew Chan will be called on to divulge everything he knows about allegations of bribery and interference in their sentencing.

The judicial commission is preparing to summons Muhammad Rifan, who on the eve of the Australians’ executions last week, made sensational claims of corruption and interference in the 2005 case.

He says the sentencing judges asked for more than $130,000 to give the men a prison term of less than 20 years – an offer later withdrawn on orders from Jakarta to impose a death penalty.

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He first aired claims in February, without elaboration, prompting the Bali Nine pair’s current lawyer Todung Mulya Lubis to file a complaint with the judicial commission.

The commission was to call Mr Lubis for a statement on Thursday but has postponed to next week, when Mr Rifan will also be called.

Commissioner Taufiqurrohman Sahuri says the investigation can go on without Chan and Sukumaran.

But given it’s now Mr Rifan’s word against the judges, his full co-operation is vital.

“He’s the key, he can’t refuse,” he told AAP.

“If a witness is summonsed properly three times and does not show up, when his testimony is crucial to the investigation, based on judicial commission law we can summons by force, with the assistance of law enforcement, with the police,” he said.

“Rifan must come, he has made statements in public that he must explain.

“Hopefully he has evidence.”

Mr Lubis had called for the April 29 executions to be halted pending the commission’s process, an argument rebuffed by President Joko Widodo who asked why the matter was only being raised then.

However, Mr Taufiqurrohman confirmed Mr Lubis’ complaint had been lodged in February, registered on April 16, and that work to seek statements began from there.

The time between the complaint and registration was normal, he said. From registration, matters were usually handled within 100 days.

The commissioner also stressed that as an ethics body, it could not have changed the death sentences of Sukumaran and Chan.

But their Australian lawyer Julian McMahon says if his clients were alive, and corruption had been proved, they would then have to be re-sentenced.

“They’ve now been killed and their evidence cannot be tested,” he said. “It is simply astonishing.”

Family and friends of Chan and Sukumaran are preparing for their Sydney funerals, to be held on Friday and Saturday.

– AAP