The US Federal Bureau of Investigation (FBI) will help investigate the case of an American blogger hacked to death in Dhaka last week, a senior police official said on Tuesday.
Avijit Roy, an 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, who lost a finger and suffered head injuries, remains in hospital.
US State Department spokeswoman Jen Psaki called it "a shocking act of violence ... horrific in its brutality and cowardice" last Friday and offered US help for the probe.
"An FBI team might come to Dhaka this week to assist in our investigations of the killing of writer and blogger Avijit Roy," said Dhaka Metropolitan Police spokesman Monirul Islam.
Bangladesh's anti-terrorism unit said it had arrested the main suspect in the case, Farabi Shafiur Rahman, in Dhaka on Monday. Rahman has been jailed in the past for his ties to the extremist Hizbut Tahrir Islamist group.
The Rapid Action Battalion (RAB) spokesman said Rahman had confessed to threatening to kill Roy. He was placed on a 10-day remand on Tuesday.
The US -based Center for Inquiry (CFI) said Roy had written an article for the next issue of its magazine in which he described getting threats from Rahman on social media after the publication of his book Biswasher Virus ("The Virus of Faith").
Avijit's killing follows a string of similar attacks in recent years in Bangladesh. In 2013, Muslim militants targeted several secular bloggers who had demanded capital punishment for Islamist leaders convicted of war crimes during Bangladesh's 1971 war for independence.
Blogger Ahmed Rajib Haider was killed that year near his home in Dhaka after he led one such protest.
In 2004, secular writer and Dhaka University professor Humayun Azad was attacked while returning home from a Dhaka book fair and later died in Germany while undergoing treatment.
Media group Reporters Without Borders rated Bangladesh 146th among 180 countries in a ranking of press freedom last year.
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