"It is a historical fact that people were killed and the then Jamaat helped these (atrocities). Motiur Rahman Nizami had supported these (atrocities) out of conviction," 72-year- old Nizami's counsel Khondaker Mahbub Hossain told the court.
The defence counsel urged the court to commute Nizami's sentence, originally handed down by the International Crimes Tribunal (ICT) in October 2014, "on grounds of old age."
Nizami filed the appeal with the SC in November 2014.
Following today's arguments in the Supreme Court, Attorney General Mahbubey Alam said it was for the first time that a war crimes convict has confessed his guilt.
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"From their submission, it appears to me that it is for the first time that the lawyers for any convicted Jamaat leader have confessed to the crimes committed during the 1971 Liberation War and appealed for only commuting the death sentence," Alam said.
Hossain, however, later told reporters that he did not admit that his client was guilty but "urged the court to reduce the penalty if he is found guilty, considering his age and health."
The four-member bench of the Supreme Court's Appellate Division, headed by Chief Justice Surendra Kumar Sinha, fixed December 7 for next hearing when the attorney general would argue for the State.
The defence submission came 10 days after Bangladesh executed two high-profile war crimes convicts: Jamaat's secretary-general Ali Ahsan Mohammad Mujaheed and Bangladesh Nationalist Party leader Salahuddin Quader Chowdhury.
Nizami likely is the last high-profile accused in war crimes trial.
According to official figures, three million people were killed during the nine-month-long independence war against Pakistan.