This is the moment a prominent Bangladeshi-American blogger was hacked to death in the street by militant Muslims after denouncing religious extremism.

Dr Avijit Roy, 42, from Atlanta, Georgia, was jumped by the gang of machete-wielding assailants last night in Dhaka, the capital of Bangladesh – leaving his injured wife standing over his bleeding body. He is well-known in Bangladesh for for his outspoken atheism.

An obscure militant group, Ansar Bangla 7, claimed responsibility for the attack, which it said was in retaliation for his ‘crime against Islam’.

The extremists also said he was singled out because he is a U.S. citizen – and characterized the vicious killing as ‘revenge’ for attacks on ISIS in Syria.

Roy was described as a 'free thinker,' by a friend

He was also said to have a 'strong voice against Islamic fanatics'

Murder: The body of Avijit Roy was found in a pool of blood after being attacked by a clever wielding gang in Dhaka, Bangladesh on Thursday night

Police said at least two men, who are believed to have links to Dhaka University, attacked Roy around 8.45pm and landed three strong, deliberate blows to the right side of his head.

They turned on his wife, Rafida Ahmed, when she tried to save him, then fled into the crowd, dumping their weapons as they ran. Police have expressed shock that extremists struck at a university book fair, which was heavily guarded.

Witnesses have even said officers and bystanders were there during the murder – but did nothing. Several onlookers told Al-Jazeera nobody intervened in the brazen attack, while even police chiefs had said they were baffled that a man could be murdered so close to the heavily-guarded area.

The United States today said the murder was ‘horrific in its brutality and cowardice’ and represents an attack on the ‘principles’ of Bangladesh.

Roy’s body was found in a pool of blood on Thursday night after the brutal attack. Ahmed, 45, is also a blogger. She is reportedly now in hospital with a deep cut to her head.

Roy, who is a naturalized U.S. citizen and also a bio-engineer, had been receiving death threats online for years.

One Muslim fanatic, Farabi Shafiur Rahman, had reportedly posted threats on Facebook last year that Roy would be killed as soon as he returned to the country.

Roy and his wife were visiting the city of Dhaka for a book fair when they were set upon opposite the Dhaka University Central Mosque. Police have said the attackers likely have links to the university.

Jubilant extremists writing on social media were quick to praise the attackers. The account for Ansar Bangla 7 made a post which linked the killing to Roy’s nationality – and American airstrikes on ISIS.

Survivor: Rafida Ahmed is pictured above being stretchered to hospital after the attack on Thursday night. Police say she was attacked after trying to defend her husband 

Home: Dr Roy and his wife, Rafida Ahmed, lived in Atlanta, Georgia, and were visiting Bangladesh when they were attacked

It said: ‘The target was an American citizen.. 2 in 1. #America recently martyred 2 of our brothers in #Khurasan & #Shaam. #Revenge+#Punishment.’

Khurasan refers to Afghanistan. Shaam is a term for Syria, where American airstrikes have been a major part of the fight against ISIS.

They also said he had been their ‘top target’, and tried to justify the killing by saying he ‘crossed his limit’ after being ‘warned many times’.

According to an autopsy report obtained by local site BDNews24, Roy was killed by three deep gashes, which cut through his skull to the brain.

Doctors examining Roy’s body said the attack had the hallmarks of professional killers, who acted with ‘planning, skill and brutality’.

BDNews24 reported that she had lost a finger in the attack and had a deep gash to her head.

Police are yet to arrest anybody over the killing – and said on Friday they still have no leads – though they think the killing is linked to the university.

Claiming responsibility: Militant group Ansar Bangla 7 said they were behind the murder - and linked it to U.S. action against ISIS

Claiming responsibility: Militant group Ansar Bangla 7 said they were behind the murder – and linked it to U.S. action against ISIS

Target: Messages posted by the militant group strongly linked the attack to his American citizenship

Target: Messages posted by the militant group strongly linked the attack to his American citizenship

Family: The couple have a daughter who is at college in the U.S. - the picture above is believed to show Roy with his wife and the young woman

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