It was third time unlucky for Indonesian cleric Abu Bakar Bashir. An Indonesia court on June 16 found Mr. Bashir guilty of terrorism charges and sentenced him to 15 years in prison. While the 72 year old maintains his innocence, his conviction is an important step in the fight against extremist Islam and terrorism in Southeast Asia; it is only a step, however. Indonesia — along with other Islamic governments and institutions — must increase efforts to promote moderation, stifle intolerance and reduce the conditions that sustain the terrorism impulse.

Mr. Bashir claims to be a simple preacher of Islam. He is much more than that. He rose to prominence in Indonesia during the country’s prodemocracy movement of the late 1990s, returning from exile in Malaysia after the Suharto regime collapsed. He became one of the most prominent Islamic voices in that period, criticizing the secular regime that replaced the aging autocrat and its close ties to the United States, while praising Osama bin Laden and his support for radical action. He dismissed charges that bin Laden was behind the Sept. 11, 2001 terror attacks, blaming them on the CIA and Israel’s Mossad.

His outspokenness and stature won him recognition as “the grandfather of Islamic militancy.” He was the spiritual leader of Jemaah Islamiyah, the Southeast Asian version of al-Qaida. J.I. is responsible for a string of terrorist attacks throughout Indonesia, including the Bali bombings in 2002 and attacks on two Jakarta luxury hotels a year later, which altogether claimed more than 240 lives.

The Indonesian government has arrested and tried Mr. Bashir three times. He was first arrested after the Bali bombings, but that prosecution was mishandled; the preacher was sentenced to just 18 months — on charges of immigration violations. Upon his release, he was immediately rearrested and charged with involvement in the Jakarta hotel bombings. That resulted in a 30-month sentence — as he was in prison during the attack, he could not have been directly involved.

Mr. Bashir was arrested a third time in West Java in August 2010, and charged with founding and financing a group called al-Qaida of the Veranda of Mecca (sometimes referred to as al-Qaida of Aceh). The group had established a terrorist training camp in Aceh, where some 100 terrorists were being prepared for a variety of attacks, reportedly including Mumbai-style assaults on Western embassies and hotels in Jakarta and assassination plots against Indonesian President Susilo Bambang Yudhoyono. The camp was raided last year and more than 100 people were arrested. Mr. Bashr was then charged with seven counts of supporting terrorism.

Mr. Bashir insists he is innocent; he was convicted, he says, by Western, anti-Islamic laws. His lawyer said he would appeal the sentence, as would the prosecutors. They sought life in prison and want a longer term. That is likely to be a moot effort. The cleric will soon go on trial for connections to the suicide-bombing of a mosque inside a police compound in Central Java that occurred last April. And at 72, Mr. Bashir is unlikely to outlive his sentence.

If the conviction is a victory in the fight against terrorism, it is by no means the end of the efforts. While unpopular among the overwhelming majority of Indonesians — and the appeal of Mr. Bashir’s message diminished considerably when it became clear that the primary victims of his program were Indonesians — there remains a significant number of people who follow the radical path.

Islamic extremism is resilient and continues to be propagated throughout the region, keen to exploit grievances real or imagined. Terrorist groups are no longer hierarchical, but have become networked, loosely linked and entrepreneurial. They can be low tech, using local materials and targets. It is, in the words of Ms. Sidney Jones, a noted expert on regional terrorist groups, “do-it-yourself jihad.”

Ultimate success in this struggle against terrorism depends first on effective law enforcement. That demands good intelligence, sensitivity to local conditions — there is no one size fits all solution to terrorism — and police who understand the threat. The presence of radical sympathizers among the police and security forces will ensure that any program fails.

It also requires that the government step up efforts to promote tolerance. Supporters of radical Islam are a minority in Indonesia, and Indonesian voters have made clear their preference for secular government in a series of elections throughout the last decade. Nonetheless, there has been a rise in religious intolerance throughout the country over the last decade, evident in both opinion surveys and the growing number of attacks on Christians and their churches. There have been lynchings of other minority religious groups as well.

The highest levels of the Indonesian government must speak out against such attacks and demand recognition of and peaceful coexistence with other religions in Indonesia. Friends and allies of Indonesia can provide aid and assistance to the police and law enforcement groups, as Japan has done in the past. Development assistance is also important as many radicals are driven down that path because they lack other opportunities. A comprehensive strategy can defeat terrorism in Indonesia; the arrest and conviction of Mr. Bashir is a critical part of that approach.

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