A prominent Bangladeshi-American blogger from Alpharetta was hacked to death, and his wife seriously injured, as they walked Thursday night through Bangladesh’s capital city of Dhaka, police said.

The attack on Avijit Roy, a Bangladesh-born U.S. citizen known for speaking out against religious extremism, occurred on a crowded sidewalk as he and his wife, Rafida Ahmed Bonya, were returning from a book fair at Dhaka University.

Bonya, who is also a blogger, was critically injured when she tried to save her husband, according to the Prothom Alo newspaper. She was transferred from Dhaka Medical College Hospital to Square Hospital, where she is listed in stable condition, the newspaper reported.

Bonya, 45, and Roy, 42, have lived in their Alpharetta subdivision since 2008, according to online records.

Roy was the founder of a popular Bengali-language blog, Mukto-mona, or Free Mind, which features articles on scientific reasoning and religion. A simple message was posted on the blog's website early Friday: "We mourn, but we are not out."

According to The Investigative Project on Terrorism, a non-profit research group that compiles statistics on radical Islamic terrorist groups, Roy had been the target of threats from Islamists over his secular views.

He and his wife were in Dhaka to attend an annual national book fair where two of Roy’s works were being promoted.

About 8:45 p.m. Thursday, a group of men ambushed the couple as they walked toward a roadside tea stall, with at least two of the attackers hitting them with meat cleavers, Dhaka police Chief Sirajul Islam said.

Jibon Ahmed, a photographer for a local photo agency, told The New York Times that he heard screams outside the book fair and after finding the couple, he helped them into an auto-rickshaw and took them to a hospital, where Roy died.

Two blood-stained cleavers were found at the scene after the attackers disappeared into the crowds.

A previously unknown militant group, Ansar Bangla 7, claimed responsibility for the attack, Assistant Police Commissioner S.M. Shibly Noman told the Prothom Alo newspaper.

The New York Times reported that in addition to his blog, Roy wrote for the website of the Center for Inquiry, a U.S.-based organization dedicated to humanist thinking and critiques of religion.

The Center for Inquiry posted the following statement on the organization’s website:

“We at the Center for Inquiry are shocked and heartbroken by the brutal murder of our friend Dr. Avijit Roy in Bangladesh, it is speculated at the hands of Islamic militants. 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.”

Tom Flynn, the editor of Free Inquiry magazine, which published articles by Roy, said Roy’s blog was the leading Bengali platform for discussion of secular and scientific ideas.

He said Roy was well aware of the dangers he faced, which reportedly included threats on Facebook to murder him if he returned to Bangladesh.

In a recent article, Roy wrote about his 2014 book, “Biswasher Virus,” or “The Virus of Faith.”

“The death threats started flowing in my email box on a regular basis,” Roy said, adding that one extremist “issued death threats to me through his numerous Facebook statuses.” In one, the extremist wrote, “Avijit Roy lives in America and so it is not possible to kill him right now. But he will be murdered when he comes back.”

Despite the risks, Flynn said, activists such as Roy often feel drawn to the places that shaped them. “There is this tremendous pull of home,” he said.

To some degree, Flynn said, writers who oppose religious extremism have grown accustomed to attacks against their peers.

“Sadly, in the Muslim world,” he said, “this is just one more tragedy in a long parade of them.”

The campaign of violence has not deterred enlightened thinkers from speaking out, Flynn said.

“What we’re seeing is brave individuals continuing to come forward and take the risk,” he said. “Dr. Roy was one of them.”

— Staff writer Victoria Hicks contributed to this report, which includes information from the Associated Press.