Muhammad's spiritual mentor in Medan was also in jail, but when the preacher decided to abandon violence and help the police instead, Muhammad turned to the sermons being broadcast in his prison cell through smuggled audio recordings and cellphones. He decided he liked what Aman was saying from his jail in Cipinang.

In some ways an "accidental terrorist", Aman has never taken part in a terrorist operation. He was arrested for the first time in May 2004 when a bomb went off while he was giving a sermon. Someone else had been conducting a bomb-making class in the house.

Sentenced to four years in prison, he began translating the Arabic works of Middle Eastern proponents of violent militant struggle. Friends posted the translations online.

In the barren intellectual field of Indonesian extremism, Aman became an immediate star. His translations were turned into books and widely discussed. His talks were recorded, inspiring many passionate new recruits throughout Indonesia, who took it upon themselves to recruit others to their self-defined militant cause.

Aman hit the lecture circuit after his release. Invited to take part in the Aceh training camp in 2009, he refused but donated money.

When the camp was discovered the next year and all its participants, instructors and financiers arrested, Aman was sentenced to 10 years' imprisonment.

He was sent to Cipinang Prison, where he was once again united with his followers, including one Sunakim, who was then almost 30.

In Cipinang, with Sunakim ready to massage his tired limbs, Aman received tens of visitors every day, acolytes seeking advice on just about everything.

They gave him food, clothes, toiletries, stationery and books, and they also typed his works for publication on a dedicated website.

The prison authorities decided to transfer him to one of the five facilities in Nusakambangan, Indonesia's Alcatraz-like island prison, in 2012.

OLD NETWORKS, NEW ALLEGIANCE

Meanwhile, Sunakim bided his time in jail, earned his remissions and was released last year for good behaviour. We now know he went back to his old terrorist network, linking up with other followers of Aman, who had switched allegiance to ISIS from prison in 2014 and has since been urging all his acolytes to strike terror in its name.

Late last year, another terrorist cell loyal to Aman based in Solo, Central Java, reached out to Sunakim, who lived in Karawang, not far from Jakarta.

According to Jakarta police chief Tito Karnavian, who used to lead the anti-terrorism unit Detachment 88, one Bahrum Naim had sent money and instructions to the Solo network from Raqqa in Syria. Bahrum, convicted of gun possession and released after 21/2 years in jail, was also an Aman groupie and, thus, an ardent supporter of ISIS.

He left for Syria last year, where he is said to have become a leader of the Katibah Nusantara unit of Malay-speaking fighters with ISIS.

It is not yet clear if Bahrum roped in Sunakim. The two had briefly shared a police detention cell in Jakarta while awaiting transfers to other prisons.

Apart from shared prison experiences, the key thread linking all the attackers and Bahrum is their blind acceptance of and fealty to the virulent ideology of hatred spawned by Aman, the most important booster for ISIS in Indonesia today.

Taking up residence in Indonesia's Alcatraz has not stopped Aman from writing and publishing his pro-ISIS screeds, and urging his followers to fight for ISIS, in Syria or at home.

PRISON DYNAMICS AND TERRORIST RECIDIVISM

In the last few years, we have been studying how terrorist convicts affect inmate dynamics in Indonesian prisons, and the motivations and factors that influence decisions by convicted terrorists to re-engage in violence upon release.

We have visited several of the 25 Indonesian prisons and detention centres that hold terrorist convicts, including Cipinang and Nusakambangan, reviewed the case histories of 40 known terrorist recidivists, and interviewed prison officials, inmates, as well as recently released prisoners. Our findings are profoundly depressing.

In the prisons where there are sizeable numbers of terrorists serving jail time, they answer to no one except themselves, deciding their own routines and complying with prison regulations and participating in so-called deradicalisation workshops only when it suits them.

Prison staff, untrained and unprepared, are content to leave them be, as riots invite too much scrutiny and terrorist inmates have instigated prison riots.

Our interviews reveal that for Indonesian terrorists, a spell in prison, rather than being an intervention stage, is seen as a way station to further glory.

Many leave prison not only unreformed, but also more influential in local militant circles.

Enter an Indonesian prison and among the first thing a visitor sees is the standard operating procedure (SOP) governing visits, framed and hung prominently on a wall. Every visitor is to show identification, register, record the name of the inmate, allow guards to pat him down and search any handcarried bags, and keep his cellphone in a locker.

SOPs are, of course, good only if they are followed consistently and guards are well trained in search procedures. Some prisons like Cipinang make a greater effort to stop contraband from being smuggled in.

But visitors are always free to bring in bags of foodstuff and other gifts for inmates. These are searched in a cursory manner.

In terms of security, Indonesian prisons, built mainly during the Dutch colonial era, have all the requisite controlled access, high walls, barbed wire, watchtowers, and closed-circuit television coverage. Escape is not impossible but curiously rare. What the building layouts do not facilitate is segregation. Overcrowding does not help either.

PRIVILEGES ENJOYED BY TERRORIST INMATES

Cipinang Prison, where some of Indonesia's leading terrorists have at one time or another been incarcerated, is one of the few prisons that technically segregates terrorist inmates from other offenders. Block D is the special block for terrorist inmates, who have their own sports facilities and a cell converted into a musholla (small mosque).

But Cipinang Prison is perpetually overcrowded and, with no extra manpower, prison staff simply allow inmates from all blocks to mingle freely during daylight hours.

There is nothing to stop terrorist inmates from going to other blocks to conduct religious study sessions or to engage in business enterprises.

Indeed, terrorist inmates have more privileges. They can be visited freely by families, friends and relatives almost every day except on Sundays.

The visits are not monitored, allowing free exchange of information. One former inmate recalled getting visits from Jemaah Islamiah (JI) members who brought him books on suicide bombing and tried to matchmake him with a woman from the network.

COMPETITION FROM OTHER TERROR NETWORKS

Ideological leaders like Aman do not, however, have free run of the prisons.

They face competition for influence from the JI hierarchy, which is more interested in preserving JI as an organisation.

Ironically, these JI leaders receive help from prison staff, who prop them up in hopes they will help the guards maintain order.

Challengers to the leaders' authority are transferred to Nusakambangan.

Jailed JI leaders thus control more than half of the terrorist inmates in Cipinang prison and are seen to be cooperative, readily sending their followers to prison-run workshops.

Terrorist inmates told us that prison provides them with time for intimacy with God.

They have time to pray, review interpretation books and study Arabic. This opportunity to practise their religion and deepen their study of Islam has led them to become more confident in their beliefs.

This is important, as many did not have an adequate understanding of Islam to begin with.

The religious activities also allow the terrorist inmates to show their religiosity, leading the prison staff and other inmates to mark them as good Muslims and, therefore, good people.

They are thus shown respect and the social status of terrorist inmates in general rises in the prison population.

Indeed, prison staff believe they can trust the more religious terrorist inmates and involve them in programmes to teach Arabic and recite the Quran in prison mosques.

An appointment as an official instructor gives terrorist inmates two advantages: official cover to socialise and interact with non-terrorist inmates, and favourable review of their applications for remission and early parole.

More importantly, the religious activities nurture the spirit of brotherhood among the terrorist inmates in an environment where their solidarity is otherwise challenged.

The spiritual bonds often translate into emotional bonds, making it easier for inmates to band together to deal with problems with prison staff.

In major prisons where terrorist inmates are housed in special blocks, leaders use group prayers and Islamic studies to consolidate their power.

They control the prayer schedule, the roster of inmates for sermons, the schedule for Islamic study sessions and even the schedules for cooking, cleaning and exercise.

Members are also expected to show their loyalty by following their leaders in fasting regularly.

The Islamic study sessions are a sort of ideological course for terrorist inmates devised by group leaders.

When Aman was in Cipinang Prison, he used to conduct regular lessons on Islamism every morning and evening. Almost all the inmates in Block D attended his lessons, including those who did not subscribe to his ideas.

He also dictated attitudes towards opponents and prison staff, and how the inmates organised themselves.

He would declare as infidel anyone he considered acting against his group.

When terrorist inmates became involved in drug trafficking in a Medan prison, for example, they received calls from Aman, chastising them for not behaving like mujahideen.

Now in Kembang Kuning Prison in Nusakambangan, he has fewer followers among fellow inmates.

But his influence has not abated.

Twice a week, his followers come from all over the country, taking long bus rides and then the prison ferry to the island, smuggling in Arabic manuscripts downloaded from the Internet for him to translate. They also record his sermons and distribute them as MP3 files, for sharing via e-mail or text messages.

The audio files are also distributed from prison to prison, so other terrorist inmates become familiar with his ISIS ideology, even if they have never met him.

• Susan Sim, vice-president for Asia of The Soufan Group, and adjunct senior fellow at the S. Rajaratnam School of International Studies in Singapore, was previously a diplomat, intelligence analyst and Indonesia bureau chief for The Straits Times from 1996 to 2002.
  Noor Huda Ismail, a PhD candidate in politics and international relations at Monash University in Melbourne, Australia, founded the Institute of International Peace Building in Jakarta and pioneered a Food for Peace programme to help former terrorists reintegrate into society.
• This is the first of a two-parter on prison dynamics and terrorist recidivism in Indonesia. The second part will be published in tomorrow's paper. It was first published online by the Brookings Centre for East Asia Policy Studies.