Two other leaders of the Jamaat-e-Islami have been sentenced to death by the tribunal.
His family and friends blamed Jamaat-e-Islami, the country's largest Islamist party, for the killing.
The issue has united Islamist parties, which have often had political and ideological differences with Jamaat-e-Islami.
Earlier this month the tribunal charged Ghulam Azam, the former leader of Jamaat-e-Islami, with war crimes.
Last week, a special tribunal sentenced a former member of Jamaat-e-Islami to death in absentia.
BBC: Bangladesh strike over war crimes trials sparks clashes
Supporters of the country's largest Islamist party, Jamaat-e-Islami, say the trials are politically motivated.
BBC: Dhaka police and protesters clash over war crime trials
In Bangladesh the fortunes of the Islamist Jamaat-e-Islami party plummeted in last December's election.
The biggest Islamic party, Jamaat-e-Islami, loathes him for breaking his promise to shed his uniform.
Jamaat-e-Islami a key partner in a former Bangladeshi government says the charges are politically motivated.
Senior Jamaat-e-Islami leader Delwar Hossain Sayeedi was convicted of murder, abduction, rape and torture, and sentenced to death.
They are being used less as a path to justice than to crush an opposition Islamic party, Jamaat-e-Islami.
Mollah and five other leaders of the Jamaat-e-Islami party have been on trial before Dhaka's International Crimes Tribunal.
Among those detained were Syed Ali Geelani, head of the fundamentalist Jamaat-e-Islami, which favors Kashmir's accession to Pakistan.
The Islamist Jamaat-e-Islami party said it withdrew its candidates in Karachi and the southern city of Hyderabad in protest.
WSJ: Irregularities at Polls, Strong Turnout as Pakistan Votes
All the 10 people charged by the tribunal so far are from opposition parties, eight of them from Jamaat-e-Islami.
Haider's family and friends suspect Jamaat-e-Islami in the attack, but the Islamic party issued a statement Saturday denying involvement.
The recent violence is mainly blamed on the opposition Jamaat-e-Islami party, whose leaders are facing war crimes at the tribunal.
The Jamaat-e-Islami wants the trial of its leaders for crimes allegedly committed during the 1971 independence war to be stopped.
BBC: Dhaka police and protesters clash over war crime trials
The ordeal proved embarrassing for Usman Sharif, a candidate for the hard-line religious Jamaat-e-Islami party, in the southern city of Karachi.
Jamaat-e-Islami was a key partner in the former government of Khaleda Zia, a longtime political rival of Prime Minister Sheikh Hasina.
Protesters are out on the streets across the country in support of Jamaat-e-Islami's strike and there are reports of sporadic clashes.
Liaqat Baloch, secretary general of Pakistan's most popular Islamic party, Jamaat-e-Islami, said members of his party were strongly considering boycotting the elections.
All of the ten people on trial are from opposition parties, eight of them from the Jamaat-e-Islami, the country's leading Islamist group.
Eight of the 10 suspects indicted by the war-crimes tribunal are from Jamaat-e-Islami, an ally of the main opposition Bangladesh Nationalist Party.
Abdul Kader Mullah, 64, the assistant secretary general of the Jamaat-e-Islami, was found guilty of five out of six charges, including murder.
Observers now expect the verdicts in the cases of senior Jamaat-e-Islami leaders such as Mr Sayeedi and Mr Azam to follow rapidly.
The Jamaat-e-Islami, Bangladesh's largest Islamist party, has been holding demonstrations demanding the immediate release of its leaders, who are facing war crimes charges.
Ten others are on trial, including eight top leaders of Jamaat-e-Islami and two members of the opposition Bangladesh Nationalist Party (BNP), one a former minister.
His Jamaat-e-Islami party had already ordered a nationwide general strike to denounce the trial, shutting down schools and shops and halting most traffic in Dhaka.
Mr Sayadee is a leader of a prominent Islamic party, Jamaat-e-Islami.
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