Rahman alias Raju Bhai, a British national of Bangladeshi origin was arrested yesterday from Vikas Marg, Shakarpur (near ITO by the Delhi Police's Special Cell, that was on his trail since July.
Rahman is trained in using hi-end weapons and has fought against the Syrian forces on behalf of Jabhat al Nusra, an affiliate of al-Qaeda in Syria.
The investigators describe him as a "trained solider fighting for a wrong cause".
Rahman's father had moved from Bangladesh to London in the 1960s and had set up his business there. His family lives in posh central London.
The 27-year-old's elder siblings are settled in London.
One of his brothers is in the banking sector while his three sisters are associated with banks and social work, the police said.
During interrogation, Rahman told police that in 2011-12, he was arrested in London for rash driving. "While he was lodged in a jail there for close to eight months, he came in contact with some people and that was where his indoctrination started," said an officer privy to the probe.
Subsequently in 2013, he travelled to Mauritania in west Africa, to "gain knowledge about religion", the police said, adding that it is suspected that he was radicalised there.
Mauritania is the stronghold of Al-Qaeda in the Islamic Maghreb (AQIM), a Salafi-jihadist militant group.
After his radicalisation, he was sent to Atmeh, Syria, where he was trained in using weapons, including AK-47, and IEDs (improvised explosive device) for close to three months.
He was sent to Aleppo where he fought against the Syrian government forces as a member of Jabhat Al Nusra, an affiliate of al-Qaeda in Syria, the police said.
In between, he also visited London where intelligence agencies questioned him for his alleged links with al-Qaeda.
He visited Dhaka and other places and radicalised dozens of young people in Bangladesh for their entry into Myanmar from Chittagong.
He came in contact with two youths Tanzeel, the son of a bureaucrat and Adnan, son of a former High Court judge.
Before he could radicalise more youths, he was arrested in September 2014 in Bangladesh on charges of terror financing and recruitment.
He was lodged in jail till April this year. While he was in jail, he came in contact with members of other terror outfits, including Jamaat-ul-Mujahideen Bangladesh, said an investigator.
After he was released on bail in April this year, he was asked to travel to India since the Bangladeshi authorities were already on his trail.
He entered India illegally in April and on the instruction of top leaders of al-Qaeda, started looking for Rohingya Muslims so that he could "radicalise" them and train them to fight against the Myanmarese army, said the investigator.
During this period, he stayed at various madrassas in Kishanganj (Bihar), Hazari Bagh (Jharkhand), NCR and other places. He had plans to set up base in Mizoram or Manipur to train radicalised youths.
Police also suspect that he was in touch with some militant organisations in Kashmir but till now, they have not found any clue whether he had any plans specific to India.
A tech-savvy person, Rahman was in touch with top leaders of al-Qaeda, Muhammad al-Jawlani, head of al-Nusrah Front through secure messaging apps like Telegram, the investigator said.
He knew how to use protected sites so that his conversations could not be deciphered by the intelligence agencies.
Police are questioning him on whether he has been successful in radicalising any Rohingya Muslims so far here and how many times he had visited Delhi.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)