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DHAKA, Bangladesh — The main suspect in the killing of a U.S. blogger and critic of religious extremism who was hacked to death last week was arrested, Bangladesh's anti-terrorism unit on Monday.

Forces from the Rapid Action Battalion arrested Farabi Shafiur Rahman, who was previously jailed for his ties to the extremist Hizbut Tahrir Islamist group, at a bus stop in Dhaka, a spokesman told reporters.

The spokesman said Farabi had confessed to threatening to kill blogger Avijit Roy. Farabi was still being interrogated.

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Roy, an American engineer of Bangladeshi origin, was killed by machete-wielding assailants on Thursday while returning from a book fair. His wife and fellow blogger Rafida Ahmed suffered head injuries and lost a finger. She remains in hospital.

Last year, Farabi posted on Facebook: "It's a holy duty of Bangalee Muslims to kill Avijit," police said.

It was the latest attack on critics of religious extremism in the Muslim-majority nation.

In 2013, religious militants targeted several secular bloggers who had demanded capital punishment for Islamist leaders convicted of war crimes during Bangladesh's war for independence.

A poster displays a portrait of Avijit Roy in Dhaka, Bangladesh, on Friday. A.M. Ahad / AP

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- Reuters