The four bloggers hacked to death in Bangladesh since 2013 are profiled here by The BBC and The Daily Star 

Avijit Roy

Blogger Avijit Roy was killed and his wife brutally hacked near TSC at Dhaka University. Photo:Collected

Avijit Roy was born to a Hindu family in 1972 in Bangladesh but had emigrated to the US. An engineer by profession, he set up his Bengali-language blog, Mukto-Mona (Free Mind) to promote secular and humanist writing in Muslim-majority Bangladesh. He was also the author of numerous books and magazine and journal articles - and had received death threats from Islamist radicals for his writings, according to his family.

He courted controversy by not only championing atheism but also tacking issues such as homosexuality which he argued was inherent in man's nature. His approach upset many in conservative Bangladesh. He regularly returned to Bangladesh for the country's annual book fair in Dhaka, which is where he was killed in February. "He was a wonderful man who through his website encouraged many free-thinking Bangladeshis to challenge conventional religious orthodoxy," one friend told the BBC.

Ananta Bijoy Das

Ananta Bijoy Das, 32, was a banker who wrote blogs for Mukto-Mona, the website once moderated by Avijit Roy. Police said that, according to writings by Das that they had collected, he also wrote about science and the evolution of the Soviet Union. A group of machete-wielding attackers hacked him to death in the north-eastern city of Sylhet in May.

A fellow blogger is reported as saying that while Das championed secularism he was mostly concerned with science, and had written a book about Charles Darwin. "He was a voice of social resistance," said Imran Sarker, head of the Blogger and Online Activists Network in Bangladesh.

Oyasiqur Rahman

Oyasiqur  Rahman, 27, blogged under the pen-name, Kucchit Hasher Channa, or Ugly Duckling. He is reported to have criticised irrational religious beliefs and is said to have written a 52-episode series for an anti-religion satirical site called Dhormockery.com which mocked aspects of Islam.

According to the International Humanist and Ethical Union, he was mild mannered in person but wrote biting satire before he was killed in Dhaka in March. Rahman wrote about religion and science mainly on Facebook, according to news website BDNews24. "I liked him for his satire, his sense of humour. He was a wonderful blogger," said Asif Mohiuddin, a fellow Bangladeshi blogger.

Ahmed Rajib Haider

A libertarian, Rajib graduated in architecture from Asia Pacific University in 2004. As a free spirit, he could not continue in a job for long. Mega Builders was his last workplace. He was born in 1980. Till class-V, he studied at a school in Iran as the family lived there for his father's job. He passed SSC from the Government Laboratory High School in Dhaka in 1996 and HSC from Kapasia Degree College in 1998.He was an activist of the Shahbagh movement demanding death penalty for war criminals and posted his blog under the nickname "Thabababa".Rajib was hacked to death in the capital's Pallabi area on February 15, 2013.