SINGAPORE - The Darusy Syahadah pesantren in Boyolali, on the outskirts of Solo city, Central Java, has long been a hub for radical recruitment and training.
Its name is Arabic for "School for Martyrs".
The former principal of the Islamic religious school, and now its chairman, is a veteran who trained in Afghanistan and Mindanao, in the southern Philippines.
Its graduates include suicide bombers and members of the Jemaah Ansharut Tauhid (JAT), a group widely seen as the successor to the Jemaah Islamiah (JI) terror group.
And it was here that Masyhadi Mas Selamat trained as a religious teacher from 2005 to 2008.
Through the school and its alumni networks, he imbibed extreme views and developed links to radicals, say sources and analysts watching the militant movement in Indonesia.
But when I visited Darusy Syahadah last Friday afternoon, the students were warm and friendly. All boys and aged 14 to 18, they smiled and said the Islamic greeting: "Peace be upon you."
The reception was quite different at another religious school, the Al-Ihsan pesantren in Madiun, East Java, which Masyhadi had attended when he was younger and returned to teach at in recent years.
Its students displayed a noticeable dislike of strangers, staring suspiciously the moment I arrived. I smiled, but they just kept staring.
Could this be the next school to watch?
Little is known about the students who are aged 12 to 15. But it does not follow the national curriculum, and its principal had apparently arranged for Masyhadi's false identification documents.
Observers note that the mid-1990s saw an exodus of students from another radical school linked to the JI network - Al-Mukmin in Ngruki, Solo - to Darusy Syahadah.
An earlier generation of Al-Mukmin graduates were behind the first Bali bombings in 2002 that killed 202 people, but Darusy Syahadah instructors and alumni were implicated in subsequent attacks.
Jabir, a Darusy Syahadah teacher, recruited the suicide bomber Salik Firdaus in the second Bali bombing in 2005 which killed 20 and left more than 100 injured.
Another former student of Darusy Syahadah, Lutfi Haedaroh alias Ubaid, a council member of the JAT, helped set up a paramilitary training camp in Aceh, and other graduates have travelled to Poso and Palu in Sulawesi for training and attacks.
Darusy Syahadah's current principal, Mr Qosdi Ridwanullah, has rebutted claims that the school teaches militancy.
"Students read other books here, and also when they are away on holidays. Sometimes they read certain books that make them deviate from good teachings," he said.
He has gone on YouTube to promote the school, saying it does not side with any single Muslim organisation but tries to be neutral and independent.
Al-Ihsan's senior instructor Fathu Shobah was evasive when approached by The Sunday Times.
But he did admit that the school cannot issue diplomas as it does not follow the national curriculum.
Analyst Sidney Jones has said that Indonesia should pay special attention to the younger siblings and children of arrested radicals at these schools, even as JI seems to be dormant.
This includes Darusy Syahadah, where analyst Taufiqurrohman said hardline views are still spread.
For example, students are taught that it is justifiable to kill those who uphold democracy as it goes against God's law, and that Muslims must prepare themselves for battle against the enemy.
"It has a massive effect on the way some of its graduates view the government and enemies of Islam," he said. "The graduates' involvement in terrorist activities has proven this."
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