The last trip he made to the country was in 2000, RAB said at a news conference on Sunday after they took him into custody from Dhanmondi on Saturday night.
Aminul was living in the Dhanmondi area from 2014 after moving houses, said Commander Khondker Al Moin, a RAB spokesman.
He and his wife lived at the house. The couple’s two daughters, now living in Singapore and Australia, were paying for their parents’ home.
Aminul was known as Rajab Ali in Dhanmondi and Kalabagan neighbourhoods.
He made several friends in Pakistan during the 1971 Liberation War and went to visit them on occasion, he said during the initial interrogation, RAB said.
In 2014, the International Crimes Tribunal filed a case against Aminul on charges of murder, genocide, kidnapping, detention, torture and looting during the Liberation War. He was indicted in 2015 and sentenced to death in 2018.
During the trial, the prosecution said Aminul received arms training at the Pakistan Army camp in Kishoreganj’s Bhairab in 1971 and later formed the local unit of Al-Badr militia to assist the Pakistani forces upon his return to his area, Alinagar village in Kishoreganj’s Austagram.
Freedom fighters reportedly caught him after independence and he was jailed for life in three cases filed under the Collaborators Act 1972.
Freed in 1981, Aminul authored a book “Al-Badr Bolchhi”.
The prosecution mentioned that his statements in the book proved the war crime charges against him.
The International Crimes Tribunal sentenced Aminul and another fugitive, Md Liakat Ali from Habiganj, to death in 2018 for wartime crimes against humanity, including murder and genocide.
According to the probe report, both of them committed several crimes in Lakhai Upazila in Habiganj, Nasirnagar Upazila in Brahmanbaria and Austagram Upazila in Kishoreganj during the war.
According to the prosecution, Liakat was an activist of the Muslim League prior to the war, while Rajab was a member of its student organisation. Aminul became the president of the Bhairab Haji Asmat Ali College unit of the Islami Chhatra Sangha in 1970.
Liakat and Aminul, supported by Pakistani soldiers, committed mass killings and looting in Krishnapur village under Lakhai Upazila in Habiganj on Sept 18, 1971.
Forty-three people, all from the Hindu community, were shot dead during their raid, according to charges pressed by the prosecutors.