Noyon Ali, arrested on October 4 for his alleged involvement in the leak told a chief metropolitan magistrate's court that Chowdhury's counsel assigned him to steal a copy of the draft verdict.
The draft was leaked a day before the tribunal sentenced Chowdhury to death on October 1 for "crimes against humanity" during the 1971 liberation war.
Chowdhury, 65, the first member of the main opposition Bangladesh National Party to be tried by the court, was found guilty of rape, torture, murder and genocide.
"He (Ali) also named two counsel and a personal staff of the convict and a fellow tribunal staff (for the misdeed)," an official of the magistrate's court told reporters.
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Immediately after the verdict announced, Chowdhury and his family members had alleged the judgement was "prepared by the Law Ministry" to be delivered by the tribunal in a pre-dictated manner while its copy was available on the internet.
Chowdhury's wife and other family members showed reporters what they claimed was the leaked version of the judgment and said it was retrieved from the computer of a senior Law Ministry official.
Tribunal officials, however, said the verdict was possibly leaked at its initial drafting stage ahead of its final revision for pronouncement.