“This is unfortunate, and this is unexpected,” Mr. Razzaq said of the verdict and sentence in a telephone interview. “This is a perverse judgment. It is inconceivable that a court of law awarded him a conviction. This prosecution was for a political purpose.”

Jamaat leaders and other opposition politicians have said for months that the government was manipulating the war crimes process to go after political rivals, accusations that the authorities deny. The proceedings have already created dissent and some international criticism. The chief presiding judge resigned after reports, based on hacked Skype conversations, that the judge had improper contacts with a legal expert linked to prosecutors and the government.

But to many Bangladeshis, the real injustice has been that war criminals have remained free for decades. On Feb. 5, the tribunal convicted another Jamaat leader, Abdul Quader Mollah, and sentenced him to life in prison. Furious that the tribunal had not sentenced Mr. Mollah to death, protesters gathered in growing numbers, surpassing 200,000 on some days.

The protests have become known as the Shahbagh movement, named for a large intersection in central Dhaka where the main demonstrations have taken place. Many political analysts say the Shahbagh protests are the most significant spontaneous political movement in Bangladesh in decades. Though the movement may be suffused with idealism and proud nationalism, it also bears a hard edge, with demands for the execution of convicted war criminals.

Sultana Kamal, a prominent human rights leader in Dhaka, said that she disagreed with the calls for the death penalty, but that they reflected the cynicism of Bangladeshis who have seen war criminals evade punishment for decades. Many people were infuriated when Mr. Mollah flashed a victory sign after receiving his life sentence.

“We have a problem in accepting that they are demanding the death penalty,” Ms. Kamal said in a telephone interview. “But we understand that it was from a nervousness among the people here that unless they are given the highest penalty in the land, these people will come back out.”