Bahrun Naim, who has been linked to the six arrested militants for planning a rocket attack on Singapore, is a leading figure with Katibah Nusantara which is the South-east Asian branch of the Syria-based Islamic State (IS).
The Indonesian authorities identified Bahrun as the mastermind of the Jakarta bombings that killed eight people earlier this year.
Officials believe that he wanted to set up an IS "province" in the Southeast Asia region, including Indonesia, the southern Philippines, southern Thailand, Malaysia and Singapore.
The 33-year-old Bahrun is believed to be from Pekalongan in Central Jawa. He worked as a computer technician and used to run an Internet cafe in Solo.
Bahrun was said to be very close to the son of Abu Bakar Bashir, a radical Islamic cleric. Bashir is serving a 15-year jail sentence at present for his involvement in a terrorist training facility in Indonesia's Aceh.
Today Online reported former Indonesian police chief Badrodin Haiti saying that when Bahrun was arrested, in February 2011, for possessing illegal arms and explosives, he revealed many things about bomb making.
"He explained and gave motivation about launching a holy war and explained how to make bombs and said that he would send money to anyone who is ready to engage in terrorist acts," Haiti said.
After 3 years, he was released and he disappeared with his wife. The police believe that last year they left for Syria and joined IS.
Bahrun emerged as a key player in militant networks since then.
Last year in a Telegram exchange with Reuters, Bahrun said he enjoyed his life in Syria and did not intend to come back.
He said, "I move around, depending on where our emir orders us to go. It's good here in Syria. There's electricity, accommodation, water and it's free. The services provided by them are good, cheaper than in Indonesia."
Bahrun runs a blog where he encourages the jihadists and offers advice to them. He has changed the blog name several times. He also praises the attacks carried out by those who have sworn allegiance to IS.
However, the blog is not accessible anymore and it is not known whether he has any other blog.