Authorities in Bangladesh have made an arrest in last week's horrific hacking death of a north Fulton County man known for his blog critical of extremist Islam.

Alpharetta resident Avijit Roy had traveled to the Bangladesh capital of Dhaka to attend a large book fair, and was leaving the fair Thursday night with his wife, Rafida Ahmed Bonya, when the two were attacked by a group wielding meat cleavers.

Roy was killed, and his wife was seriously injured.

Monday, Bangladeshi security officials arrested Farabi Shafiur Rahman, a Muslim blogger who had reportedly threatened Roy on Facebook, saying, “Avijit Roy Lives in America, so it’s not possible to kill him right now. But he will be killed when he comes back.”

While Rahman has acknowledged making the threats, authorities have not said if they believe he was one of Roy’s attackers.

The Bangladesh government has accepted a U.S. offer of FBI help in the investigation, Foreign Minister A.H. Mahmood said.

Both Roy, who had a doctorate in engineering, and his wife, who is also a blogger, were strong atheists, said Zaydul Hoque, another Bangladeshi engineer who lives in north Fulton and is Bonya’s ex-husband.

Hoque, who described himself as a liberal Muslim, credited Roy with being an excellent stepfather to his daughter, of whom his ex-wife had custody.

“I am very sorry and very hurt because my daughter is crying all of the time because he was a good person,” Hoque said.

Bonya met Roy while he was completing his doctorate in Singapore in the early 2000s and she later brought him back to the United States, Hoque said. His ex-wife’s hostility to religion — Islam, Christianity, Hinduism, Judaism — was one of issues that undermined their marriage, he said.

“They were good people — it was only where they came to the religion issue that was tough if you were a religious person,” Hoque said. “If you are a religious person no matter what religion you followed you would have a hard time with them.”

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

— Information from the Associated Press was used in this report.