Indonesian intelligence has traced phone calls originating from the country's Nusakambangan maximum-security prison, where terrorists Aman Abdurrahman and Iwan Darmawan Muntho, alias Rois, are serving jail time, to Raqqa in Syria.
The two men, currently being investigated by the police for their part in the planning of the Jan 14 attack in Jakarta, are said to have been on the line with someone in the stronghold of Islamic State in Iraq and Syria (ISIS).
This was revealed by Coordinating Minister for Political, Legal and Security Affairs Luhut Pandjaitan during a working visit to Serang, in Banten province, yesterday.
Another government official, who asked not to be named, later told The Straits Times that the calls to Raqqa were uncovered by forensic investigators who were examining 14 mobile phones seized from a jail cell shared by Aman and Rois.
The phones were found as the two were being moved into isolation on Feb 8 in a bid to curb their influence beyond the prison walls.
The calls were apparently traced to a mobile phone used by Bahrun Naim, an Indonesian militant now in Raqqa fighting alongside ISIS.
Mobile phone data also showed that Bahrun was in touch with other militants in Indonesia before the hit on the capital, said the official. They include Dian Joni Kurniadi, one of the "Jakarta Four" attackers, as well as Muhammad Saifuddin Umar, alias Abu Fida.
Abu Fida is serving a three-year jail term after he was deported from Istanbul in August 2014. The Turkish authorities had caught him trying to cross over to Syria to join ISIS.
He, too, had allegedly contacted Rois in prison to arrange for the funding of the Jan 14 attack, the government source said.
Rois, who is on death row for his part in the bombing of the Australian Embassy in Jakarta in 2004, had apparently taught the Jakarta Four assault tactics when they visited him and Aman in Nusakambangan before the attack in January.
Mr Luhut said Banten seems to be the home town of several terrorists such as Rois and Imam Samudra, who was executed for his role in the 2002 Bali bombings that killed 202 people, including many foreigners.
To underline how radicalisation is tied to poverty, Mr Luhut shared with reporters details about Sunakim, alias Afif, one of the four militants killed during the Jan 14 attack.
Sunakim had lost six of his siblings when they were very young because his parents could not afford proper healthcare, and somehow Sunakim turned to extremism later in life.
"I believe that if we succeed in fighting poverty, we will greatly reduce radicalism," he said.
Mr Luhut said that the government plans to double its spending to 47 trillion rupiah (S$5 billion) this year on infrastructure development and other projects for grassroots groups from more than 74,000 villages across Indonesia in a bid to fight poverty.
He called on local elected leaders to ensure money from the Village Funds Programme is being used effectively to improve the lives of people struggling with poverty.
"If we are successful in fighting poverty, we would be able to prevent future (people like) Rois from emerging," Mr Luhut said.