Machete-wielding assailants hacked to death an American blogger in the Bangladeshi capital, Dhaka, in the latest of a series of attacks in the South Asian nation on writers who support free expression.
The attack comes amid a crackdown on hard-line armed groups, which have increased their activities in Bangladesh in recent years.
Avijit Roy, a U.S. citizen of Bangladeshi origin, and his wife and fellow blogger, Rafida Ahmed, were attacked on Thursday while returning from a book fair at Dhaka University. Ahmed was seriously injured. It was the latest in a series of recent attacks on secular writers in Bangladesh.
Police retrieved two machetes from the site but have not yet identified any suspects.
They said they were investigating the involvement of Ansarullah Bangla Team, a group based in Bangladesh that claimed responsibility on Friday for the murder.
Roy's family said he had received threats in recent weeks because he maintained a blog, Mukto-Mona ("Free mind"), that highlighted humanist and rationalist ideas and condemned religious intolerance.
"Islamist radicals are behind my son's murder," his father, Ajay Roy told reporters on Friday after filing a murder case with police.
"We mourn, but we are not out," read a black banner on the site.
In an interview with Al Jazeera, human rights activist Khushi Kabir questioned police inaction during the attack. Witnesses said that police and onlookers were present during the attacks, but no one came to help the victims. Police were not immediately available to comment on the accusation.
The Center for Inquiry, a U.S.-based nonprofit group that Avijit Roy wrote for, said it was "shocked and heartbroken" by the murder.
"Dr. Roy was a true ally, a courageous and eloquent defender of reason, science and free expression, in a country where those values have been under heavy attack," it said in a statement.
While the U.S. has not made a statement about Roy's death, it has condemned recent violence, including deadly bus burnings and train derailments, in Bangladesh. "The United States is gravely concerned by the ongoing unrest and violence in Bangladesh," State Department spokeswoman Marie Harf said in a statement on Feb. 5. "All Bangladeshis must have the right and the ability to express their views peacefully."
The Washington-based non-profit Committee to Protect Journalists called on Prime Minister Sheikh Hasina's government to investigate the attack and prosecute Roy's killers.
“This attack is emblematic of the culture of impunity that pervades Bangladesh, where the lack of accountability in previous attacks on the press continues to spurn a deadly cycle of violence,” said CPJ Asia program coordinator Bob Dietz in a release.
Media group Reporters Without Borders placed Bangladesh 146th among 180 countries in a ranking of press freedom last year.
In 2013 religious groups targeted several secular bloggers who demanded capital punishment for Islamist leaders convicted of war crimes during Bangladesh's war for independence.
Blogger Ahmed Rajib Haider was killed that year in a similar attack near his home in Dhaka after he led a protest demanding capital punishment.
In 2004, Humayun Azad, a secular writer and professor at Dhaka University, was also attacked while returning home from a Dhaka book fair. He later died in Germany while undergoing treatment.
Roy founded the popular Bengali-language blog Mukto-Mona, which featured articles on scientific reasoning and religion. He defended atheism in a January posting on Facebook, calling it "a rational concept to oppose any unscientific and irrational belief."
Protesters said the attack on Roy and his wife happened partly because of the government's failure to prosecute previous similar attacks.
"The government cannot avoid its responsibility as it has failed to try similar crimes before," Anwar Hossain, a university professor, told Al Jazeera.
Anujit Roy, his younger brother, said Avijit Roy went to Bangladesh earlier this month and had planned to return to the U.S. in March.
Baki Billah, a blogger and a friend of Avijit Roy's, told Independent TV that Roy had been threatened by people upset by his writing. "He was a free thinker. He was a Hindu, but he was not only a strong voice against Islamic fanatics but also equally against other religious fanatics … We are saddened. We don't know what the government will do to find the killers. We want justice.”
Islam is Bangladesh's state religion, but the country is governed by secular laws.
Al Jazeera and wire services. Mahmud Hossain Opu contributed to this report.