The alleged leader of South East Asian militant group Jemaah Islamiah (JI), Zarkasih, has gone on trial in the Indonesian capital, Jakarta.
Zarkasih is charged with conspiring to commit terrorism and supplying weapons and training to JI members.
The 45-year-old was not required to enter a plea. He could face the death penalty if found guilty.
JI is blamed for attacks across Indonesia, including the 2002 Bali bombings in which 202 people died.
Zarkasih was arrested on the island of Java in June, shortly after the arrest of another key JI figure, Abu Dujana, who is also on trial.
The two arrests were seen as a major blow to the militant network.
Shortly after his arrest, police showed reporters a video of Zarkasih apparently admitting to being the head of JI.
He said he was chosen as caretaker leader of the network in 2004 until someone more suitable could be found.
Police have accused Zarkasih, who goes by one name, of masterminding attacks across the country.
He is accused of arranging the movement of arms and explosives to Poso in Sulawesi, the scene of violent conflict between Christians and Muslims between 1999 and 2003.
The authorities also believe that Zarkasih and Abu Dujana helped to hide Malaysian fugitive Noordin Top, who was believed to have been a central figure in the Bali bombings.
His trial is the latest development in a crackdown against JI, which aims to create an Islamic state across South East Asia.