JAKARTA, Indonesia — Indonesian authorities said Monday that a top terror suspect arrested last week was the architect of a series of deadly attacks and sectarian conflicts in the world’s most populous Muslim nation.

Aris Sumarsono, known as Zulkarnaen, was arrested Thursday by counterterrorism police in a raid at a house in East Lampung district on Sumatra island.

“He was the military commander of Jemaah Islamiyah,” National Police spokesperson Ahmad Ramadhan said at a news conference in the capital, Jakarta. “He’s been on the police wanted list for 18 years.”

Zulkarnaen, a biologist who was among the first Indonesian militants to go to Afghanistan in the 1980s for training, was an instructor at a military academy there for seven years, Ramadhan said.

Since May 2005, Zulkarnaen has been listed on an al-Qaida sanctions list by the U.N. Security Council for being associated with Osama bin Laden or the Taliban.

The Security Council said that Zulkarnaen, who became an expert in sabotage, was one of al-Qaida’s representatives in Southeast Asia and one of the few people in Indonesia who had had direct contact with bin Laden’s network.

It said that Zulkarnaen led a squad of fighters known as the Laskar Khos, or Special Force, whose members were recruited from among some 300 Indonesians who trained in Afghanistan and the Philippines.

Zulkarnaen was appointed the head of Camp Saddah, a military academy in the southern Philippines established for fighters from Southeast Asia, the Security Council said. He spent a decade at the camp training other Jemaah Islamiyah members.

He became operations chief for Jemaah Islamiyah after the arrest of his predecessor, Encep Nurjaman, also known as Hambali, in Thailand in 2003.

The United States’ “Rewards for Justice” program had offered a bounty of up to $5 million for his capture. He was the only Indonesian on the list.

Indonesian police said he masterminded church attacks that occurred simultaneously in many Indonesian regions during Christmas and New Year’s Eve in 2000 that killed more than 20 people.

Ramadhan said Zulkarnaen is suspected of being involved in the making of bombs used in a series of attacks, including the 2002 Bali bombings that killed 202 people, mostly foreign tourists, and a 2003 attack on the J.W. Marriott Hotel in Jakarta that killed 12.

Zulkarnaen was also the mastermind of a bomb attack on the official residence of the Philippine ambassador in Jakarta in 2000 that killed two people, a 2004 suicide attack outside the Australian Embassy that killed nine, and a 2005 bombing in Bali that killed 20, Ramadhan said.

He said Zulkarnaen was also the architect of sectarian conflict in Ambon and Poso from 1998 to 2000.

Conflicts between Christians and Muslisms in Ambon, the provincial capital of the Molluca islands, left more than 5,000 people dead and half a million displaced. The Muslim-Christian conflict in Poso, known as a hotbed of Islamic militancy on Indonesia’s Sulawesi island, killed at least 1,000 people from 1998 to 2002.

Police previously said they were tipped off to Zulkarnaen’s location in raids after interrogating several suspected militants arrested late last month.

Zulkarnaen is also accused of harboring Upik Lawanga, another bomb maker and a key Jemaah Islamiyah’ member. Lawanga was arrested by counterterrorism police in Lampung late last month. He had eluded capture since 2005 after being named as a suspect in an attack that killed more than 20 people at a market in Poso.

A court banned Jemaah Islamiyah in 2008, and the group was weakened by a sustained crackdown on militants by Indonesia’s counterterrorism police with U.S. and Australian support. A new threat has emerged in recent years inspired by Islamic State group attacks abroad.

Indonesia’s last major militant attack was in May 2018, when two families carried out suicide bombings in the country’s second-largest city, Surabaya, killing a dozen people, including two young girls whose parents had involved them in one of the attacks. Police said the father of the girls was the leader of a militant Jemaah Anshorut Daulah cell who pledged allegiance to Islamic State group leader Abu Bakr al-Baghdadi.