All the dead were lawyers working at the Gazipur Bar Association offices in Gazipur, a city near the capital. About 100 people were injured in the blast.
The bomber was dressed as a lawyer which meant he aroused little suspicion when he entered the building around 9:45 a.m., bdnew24 reported.
The men sentenced to death by hanging are members of the banned organization Jamaatul Mujahedin Bangladesh -- Assembly of Holy Warriors, bdnews24.com reported.
The men reportedly helped make the bomb and planned the attack.
Another case relating to the bombing is working its way through the courts.
The incident was described at the time as Bangladesh's first suicide bombing, the BBC reported.
Three months before the November attack, more than 300 explosions took place on the same day in 50 towns, including Dhaka, the BBC said.
JMB leader Abdur Rahman and deputy leader Siddiqul Islam, known as Bangla Bhai, were among six JMB militants hanged in 2007 for coordinating the August 2005 attacks.
The JMB was founded near Dhaka by the Afghan-trained Rahman in 1998.
Rahman's main goal was to set up a non-secular state based on Sharia law.
The organization was banned by the government in February 2005 after attacks on non-government organizations.
A report by the Christian Post in December 2005 said Christians and Christian institutions also were under threat from the JMB.
Soon after the November attacks, the United States asked Bangladesh to expand its search for leaders of the JMB.
There also was concern among Bangladeshi media politicians weren't taking the threat seriously, a report by Reporters Without Borders said in December 2007.
The report, done jointly with the Bangladesh Center for the Development of Journalism and Communication, said at least 50 journalists and 10 publications had been threatened by terrorist groups in the past four months.
The reason was supposedly anti-Islamic articles, written by journalists, "yet the government seems unable to restore confidence in the face of this new danger for the media," the report said.
"At least 55 journalists have received death threats since September from Jamaatul Mujahedin Bangladesh, an Islamist group that has also promised to blow up eight newspapers and three press clubs."
A March 2010 report by International Crisis Group said JMB's links to the banned Pakistani group Lashkar-e-Toiba "remain a particularly serious concern."
The threat from JMB is heightened by its links to other Bangladeshi and international jihadi groups and to members of the Bangladeshi diaspora in Britain, the ICG reported.
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