Dhaka, Jul 5 (PTI): A Bangladeshi politician, whose son was one of the suspected Islamic State militants who slaughtered hostages at a cafe here, has said he was "stunned" to learn about his son's involvement in the assault as there was nothing to indicate that the boy was being radicalised.

"I am stunned to learn this, dumbfounded," Imtiaz Khan, a former leader of the ruling Awami League, told BBC Bengali.

"My son used to pray five times a day from a young age. But we never imagined this. There was nothing at home, no books or anything to indicate he was leaning that way, So we had no inkling," he said.

Imtiaz's son Rohan was shpt dead by security forces during a joint operation to free the hostages at the Holey Artisan Bakery.

Rohan's parents filed a missing person's report with the police after he disappeared last December and had not heard from him since. But they recognised him from photographs of the attackers that have been published in the local media.

Imtiaz's statement came after it emerged that attackers are all Bangladeshis from rich families and with good educational background.

Three of the attackers have attended elite private schools in Dhaka. Nibras Islam was said to have studied in Turkish Hope School, an international private school in Bangladesh, then studied in North South University, a top private university in Dhaka.

He later allegedly attended Monash University at its Malaysia campus, according to information on his social media page.

Meer Saameh Mubasheer and Rohan both reportedly attended Scholastica, a private English school.

Friends, former classmates and other acquaintances have come forward to identify the attackers after the SITE Intelligence Group published photos of the five gunmen.

Islam was active on both Twitter and Facebook before he went missing, and was revealed to have disappeared on 3 February through posts on his Facebook wall.

Analysts found a common peculiar history among all the five attackers in their 20s as they went missing between three and six months ago.

Investigators earlier said one of the youths appeared to have led the massacre studied at a madrassa education in a village in northwestern Bangladesh.

After the identities of the attackers were revealed, police asked to change lifestyle and keep an extra eye on their children to prevent them from being radicalised.

Islamic State has claimed responsibility for the killing of the 20 hostages and two police officers during the 12-hour siege that ended after the army stormed the cafe popular with expats in the diplomatic zone here, killing six attackers and capturing one alive.

Hostages who were killed include 19-year-old Indian girl Tarishi Jain. Nine Italians, 7 Japanese, one American of Bangladeshi origin, and two Bangladeshis were also among the people who were killed.