"Mukhlas… often gave teachings from the Kerobokan prison in Bali through his handphone to the congregation in Poso," the police statement said.
Imam Samudera chatted online from his
cell about funds for future attacks [EPA]
Mukhlas became known as "the smiling bomber" after he grinned and punched the air when the judge in his trial sentenced him to death.
Last year, police revealed that Imam Samudra, also on death row for the Bali attacks, had made online contact with co-conspirators about raising funds for attacks using a laptop in his prison cell.
Observers say corrupt Indonesian prison guards are easily bribed to turn a blind eye to such practices.
Indonesian police and Western intelligence officials say both Mukhlas and Imam Samudra were members of Jemaah Islamiah, a radical Southeast Asian group they say has ties to al-Qaeda.
JI has been blamed for a series of bombings and other attacks in Indonesia in recent years, including the 2002 Bali blasts.