Dhaka: February 27, 2015. A case has been filed accusing anonymous assailants of the brutal killing of writer and blogger Avijit Roy last night at Dhaka University area. Victim’s father Ajay Roy, a physics teacher at the University of Dhaka, filed the lawsuit against unidentified assailants with the police station around 9:15am today, Sirajul Islam, officer-in-charge of Shahbagh Police Station told The Daily Star Online. However, he did not tell how many people were accused in the case. “Detective Branch (DB) of police have already begun their investigation to find the motive of the killing and arrest of the culprits involved," the OC added. Assailants brutally hacked blogger Avijit Roy and his wife Rafida Ahmed Banna last night after the couple came out of the Ekushey Boi Mela around 8:30pm. They were rushed to Dhaka Medical College Hospital where Avijit died around 10:20pm. Banna, herself a writer and blogger, is undergoing treatments there in critical condition. According to AFP; A prominent American blogger of Bangladeshi origin was Thursday hacked to death with machetes in Dhaka by unidentified assailants, police said, with his family saying the atheist writer had received numerous threats from Islamists. The body of Avijit Roy, founder of Mukto-Mona (Free-mind) blog site which champions liberal secular writing in the Muslim-majority nation, was found covered in blood after the attack which also left his wife grievously wounded. "He died as he was brought to the hospital. His wife was also seriously wounded. She has lost a finger," local police chief Sirajul Islam said, adding that the attack occurred when the couple were returning from a book fair. Roy, said to be around 40, is the second Bangladeshi blogger to have been murdered in two years and the fourth writer to have been attacked since 2004. Hardline Islamist groups have long demanded the public execution of atheist bloggers and sought new laws to combat writing critical of Islam. "Roy suffered fatal wounds in the head and died from bleeding... after being brought to the hospital," doctor Sohel Ahmed told reporters. Police have launched a probe and recovered the machetes used in the attack but could not confirm whether Islamists were behind the incident. But Roy's father said the writer, a US citizen, had received a number of "threatening" emails and messages on social media from hardliners unhappy with his writing. "He was a secular humanist and has written about ten books" including his most famous Biswasher Virus (Virus of Faith), his father Ajoy Roy told AFP. Roy's killing sparked strong condemnation from his fellow writers and publishers. "The attack on Roy and his wife Rafida Ahmed is outrageous. We strongly protests this attack and are deeply concerned about the safety of writers," Imran H. Sarker, head of an association for bloggers in Bangladesh, told AFP. Pinaki Bhattacharya, a blogger and friend of Roy, claimed one of the country's largest online book retailers was being openly threatened for selling Roy's books. "In Bangladesh the easiest target is an atheist. An atheist can be attacked and murdered," he wrote on Facebook. Atheist blogger Ahmed Rajib Haider was hacked to death in 2013 by members of a little known Islamist militant group, triggering nationwide protests by the tens of thousands of secular activists. After Haider's death, Bangladesh's hardline Islamist groups started to protest against other campaigning bloggers, calling a series of nationwide strikes to demand their execution, accusing them of blasphemy. The secular government of Prime Minister Sheikh Hasina reacted by arresting four bloggers including the "militant atheist" who was allegedly attacked by the same Islamist group accused of the murder. The government also blocked about a dozen websites and blogs to stem the furor over blasphemy, as well as stepping up security for the bloggers. Bangladesh is the world's fourth largest Muslim majority nation with Muslims making up some 90 per cent of the country's 160 million people. A tribunal has handed down a series of verdicts against top Islamists and others for crimes committed during the war of independence from Pakistan in 1971.