An alleged mastermind of the 2002 Bali bombings was extradited from Pakistan to Indonesia on Thursday, after his arrest in the town where Osama bin Laden was killed, a security official said.
Indonesia's counter-terrorism agency chief Ansyaad Mbai confirmed that Umar Patek had arrived under tight security after an overnight flight from Pakistan, and ahead of an expected trial on terrorism-related charges.
"He's been detained at a detention facility... He's a very important suspect. It's hard to rank him but you can say he's a big fish," Mbai told AFP.
Patek is expected to face trial over attacks including the Bali bombings that killed 202 people and Christmas Eve church bombings that killed 19 people in 2000, the counter-terrorism chief said.
"We still have to investigate further but it's likely he will be charged over the Christmas bombings and the Bali bombings, as well as others," Mbai said, adding that Patek had confessed to involvement in both attacks.
The fatalities in the bombings of tourist bars and nightclubs on the resort island of Bali, which thrust Muslim-majority Indonesia into the front lines of the "war on terror", included 88 Australian holidaymakers.
Police say Patek, 41, worked closely with the attack's mastermind, Indonesian extremist Dulmatin, and built the massive bombs that flattened several buildings along the Kuta beach tourist strip.
Officials said murder could be the most serious crime he is charged with, as his alleged crimes were committed before the Southeast Asian archipelago passed its tough anti-terrorism law. Even so, he could still face the death penalty.
Indonesian police killed Dulmatin last year and three of his Bali accomplices were executed by firing squad in 2008. Until his arrest Patek was the last "big fish" still at large over the Bali bombings.
The Bali attack was the work of Al-Qaeda-linked regional extremist group Jemaah Islamiyah, and Indonesian officials are hoping Patek will give valuable information on JI and other Southeast Asian terror networks.
"From the very beginning his links were with Jemaah Islamiyah, which we know is linked to Al-Qaeda," Mbai said, adding that Patek was being "cooperative".
Patek is also believed to be indirectly associated with Indonesian terror suspect Hambali, who is in US custody at Guantanamo Bay, and radical Indonesian cleric Abu Bakar Bashir, who was recently convicted on terror charges.
Defence Minister Purnomo Yusgiantoro said previously there was information that Patek had been trying to meet bin Laden in Abbottabad before his arrest on January 25, but this has not been confirmed.
Foreign Minister Marty Natalegawa said last week that Indonesia did not want Patek's trial to turn into a circus.
"We do not want to create self-fulfilling... attention to a person who doesn't deserve publicity," he said.
Australia has warned that Patek's arrest could spark revenge attacks against Westerners in Indonesia, the world's most populous Muslim-majority state.
National Police spokesman Anton Bachrul Alam said security had been stepped up after Patek's extradition.
"We have prepared tight security because Umar Patek is a terrorist leader. He's highly rated so we're always on the alert and ready to ensure security," he told reporters.
Patek is also wanted in the Philippines, where he allegedly plotted attacks with militants after fleeing Indonesia.