In their minds, they were on the path towards righteousness. They were furthering the cause of Islam and becoming good Muslims.

But for some rehabilitated former Jemaah Islamiah (JI) detainees, all of whom are referred to by pseudonyms, that path was one of darkness and destruction, and plots to destroy parts of their homeland.

The clandestine group, which had a presence in Singapore since the late 1980s, had a systematic process of talent-spotting that involved casting its net under the guise of religious classes.

For Alif, who is now in his 40s and works as a dispatch rider, his first steps to radicalisation started in the home of a JI member conducting Arabic lessons.

After lessons ended, the class, which included JI leader Ibrahim Maidin, would discuss Islam. Alif recalled how Ibrahim would drive home the point that Muslims will have problems in their lives until a caliphate is established. "This is how he slowly convinced us. He told us, if we want to know more about this, then we have to organise classes to tell us more about Islam, what Islam wants us to do."

Former detainee Adam, who is in his early 60s and works in the transport sector, attended similar home-based discussions. Wanting to be a better Muslim following his marriage, he sought out religious lessons and attended ones conducted by JI spiritual leader Abu Bakar Bashir and other visiting foreign preachers like Abu Rusdan.

Adam was inspired by their passion, which fuelled his desire to want to die as a martyr and participate in jihad, or armed struggle.

Salleh, another former detainee who also attended lessons by foreign preachers, found them to be not only charismatic, but also convincing. Their explanation on jihad was one he had never heard local religious teachers talk about, and made him believe establishing an Islamic state was a religious duty.

"Their arguments and my limited knowledge of the issues they discussed at that time made me believe that what they told me was the truth... I trusted them and did not question whatever they taught me," he said.

Adam, Alif, Salleh and the other former detainees The Sunday Times spoke to said they were so inspired by these leaders that they were convinced to take a bai'ah, or oath of allegiance.

Some lied to their family members that they had to travel for work to take this oath in Malaysia, where JI leaders Abdullah Sungkar, and later Bashir, were based. The bai'ah was a pledge to be loyal to these leaders and obey all instructions they were given, and breaking it was a grave offence. It was a bond that brought new members into an inner, trusted circle.

Religious teaching continued, but with an emphasis on legitimising armed violence and terror. The end goal was to create a caliphate that obeyed God's law, as they interpreted it.

In the case of Alif, it led to an opportunity to train with Al-Qaeda in Afghanistan in the late 1990s alongside aspiring fighters from around the world. He rubbed shoulders with its founder Osama bin Laden, the architect of the Sept 11, 2001, attacks on the United States.

Alif recalls Osama as a quiet and calm man when he listened to his sermons at the training camp. "He was very tall, very fair, and he was left-handed. You can see that his eyes were always moving around, and he seemed very calm... not very fierce," he said.

Another JI member who went overseas was Helmi, a logistics worker in his 50s who had been a member of JI since 1994. After several rounds of paramilitary training in Johor between 1996 and 1999, he spent three months at Camp Hudaibiyah in Mindanao, in the Philippines, located within the camp of the Moro Islamic Liberation Front. He learnt bomb-making, weapons-handling and guerilla tactics, and performed sentry duties.

The JI members knew they were part of an illegal organisation planning criminal activities, and took great pains to make sure they were not discovered.

After 9/11, Johan, a former JI member who is now in his 60s, said members were told to shave their beards - a move right out of the playbook of the hijackers to avoid suspicion.

During meetings in members' homes, footwear was placed inside so as to not arouse the suspicion of neighbours. These discussions were never always in the same place, said Adam, who remembers how locations for their planning meet-ups kept changing to avoid alerting others in the area.

The use of codenames was the default, and JI members were taught a system of code numbers to be used when they were communicating via pagers.

When it came to stake-outs, meetings and classes, members made sure to park their vehicles at a distance before making their way to their destination. If a lift was involved, they would not take it directly to the intended floor, but would get off a few levels above or below and take the staircase.

"Sometimes in the flat, when we have some meetings, we didn't allow our spouses to listen in. So they would not know what our activities were, or what we had been discussing about," said Adam.

Around the mid-1990s, the local JI group began looking at staging attacks here.

Johan said the Sept 11 attacks were a strong motivating factor for the JI to push on with its terror plans. "We felt happy with the successes of Al-Qaeda. JI members here were envious, we felt we could do something to show our capabilities too," he said.

Shortly after 9/11, Ibrahim Maidin issued JI members here a survey to determine their level of commitment to the cause of establishing a caliphate, and to supporting terror operations overseas.

The survey asked if they were ready to sacrifice their lives in carrying out attacks against US interests. Several JI members had indicated in the forms that they were willing to die for the cause.

But the attacks could not happen overnight, and members were assigned different tasks to prepare.

Alif, for instance, was tasked by foreign JI bomb-maker Fathur Rahman al-Ghozi, alias Mike, to obtain ammonium nitrate to make the bombs and to source a place to store the chemicals.

The chemical is a controlled item here, and he would have needed to register a company to bring it in. "It is not so easy, you need to have paperwork to bring the thing here, because usually cleaning companies will order this thing," said Alif.

JI had about four tonnes of ammonium nitrate in storage in Johor, but six times the amount was needed for their plans. Some of the places Alif considered to use as storage spots for the chemical included shophouses in Onan Road in Joo Chiat.

Alif and Adam were also involved in reconnaissance work. They would stake out potential targets for attack. Such work started before 9/11 and targets like embassies were chosen to inflict as much damage as possible to the reputation of the US and its allies.

Details of these plots were discovered only when the authorities moved in on the first batch of JI members in December 2001.

Officers from the Internal Security Department (ISD) seized documents on the attack plots and bomb-making information, as well as photographs and surveillance video of the intended targets, including the embassies and government buildings. Fake passports and forged immigration documents were found too.

Among the first group of 15 individuals picked up that month was local JI leader Ibrahim Maidin, then a condominium manager.

The news sent shockwaves through the group, and panic gripped members when they heard of the arrests of their comrades.

Some like Adam and Alif were arrested later that month, and some like Salleh were caught in 2002.

Their detention under the Internal Security Act would mark a new chapter in their lives.

After the initial interrogations by investigators uncovered they had been deeply radicalised and indoctrinated, religious counsellors were roped in to help them turn away from the JI and its teachings.

In an interview, Salleh said these sessions helped him understand where JI went wrong, and how to contextualise Islam to Singapore.

"I had been misled by JI's mis-interpretation of the concept of jihad, to the point that I supported armed jihad," he said. "But Muslims in Singapore are not oppressed and we are free to observe and celebrate key religious practices and festivals without restrictions."

As for Johan, he said he had been brainwashed by the JI that the ISD would torture members and make them insane, but he experienced neither in the six years he was detained, which he described as a blessing in disguise.

"Hopefully, this can be a lesson to everybody that this danger is real," he said of the temptation of radicalisation and groups like the JI.

"You have to be cautious of that and always keep track of the mainstream teaching of Islam."