"The appeal is allowed," ruled chief justice Mozammel Huq, who headed a six-member bench of the Appellate Division, turning down the 2008 High Court judgement in this case.
The High Court had acquitted sacked junior commissioned officers Marfat Ali Shah and Abdul Hashem Mridha in 2008.
The state attorneys submitted a petition challenging the acquittal of several accused five months ago.
The four leaders - Syed Nazrul Islam, Tajuddin Ahmad, AHM Qamruzzaman and Captain Mansur Ali - were brutally killed inside the high security Dhaka Central Jail in captivity by a group of army men.
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Islam was the acting President and Ahmed performed as the Prime Minister of the then government in exile in India while two others were senior ministers of the interim administration to steer the 1971 Liberation War in absence of Sheikh Mujibur Rahman, who was in captivity in Pakistan at that time.
The post coup administration installed by the putsch leaders had put them behind the bar as they declined to support the "illegitimate government" and eventually killed just ahead of a counter-coup that ousted the August plotters.
The then self-proclaimed president Khandker Mushtaq Ahmed, however, had constituted visibly a "show case" enquiry commission to investigate into the carnage, though prosecution evidence suggested he himself had ordered the assassins entry inside the prison to kill the four leaders.
The Metropolitan Sessions Judge's court in October, 2004, originally sentenced to death three fugitive former military personnel and life term to 12 others for the jail massacre while it had acquitted four politicians and another former military officer.
Several of the suspects of the jail killings, however, were convicted and already executed under a separate judgment in Bangabandhu Murder Trial four years ago.
But the family members and the prosecution lawyers were not satisfied even with the lower court verdict in the jail killing trial as the belated trial began in 1996 alongside the Bangabandhu Murder Case.