text: DHAKA, March 2 Bangladesh's anti-terrorism unit said it had arrested on Monday the main suspect in the killing of a U.S. blogger who was hacked to death in Dhaka last week in the latest attack on critics of religious extremism in the Muslim-majority nation. 
   
   Forces from the Rapid Action Battalion (RAB) 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 RAB spokesman told reporters. 
   
   The spokesman said Farabi had confessed to threatening to kill blogger Avijit Roy. Farabi was still being interrogated. 
   
   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 suffered head injuries and lost a finger. She remains in hospital. 
   
   The police said Farabi was arrested in 2013 for social media comments that supported the murder of another blogger, Ahmed Rajib Haider, but he was later released on bail. Last year, Farabi posted on Facebook: "It's a holy duty of Bangalee Muslims to kill Avijit", the police added. 
   
   Roy's killing comes amid a crackdown on hardline Islamist groups, which have increased activities in recent years in the South Asian 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. 
   
   Media group Reporters Without Borders rated Bangladesh 146th among 180 countries in a ranking of press freedom last year. (Editing by Miral Fahmy) ||||| Story highlights Police say the suspect posted photos of the crime scene 
   
   He also threatened Roy in social media posts, his family said 
   
   Dhaka, Bangladesh (CNN) Bangladesh authorities say they have arrested the prime suspect in the murder of American blogger Avijit Roy who was hacked to death on a Dhaka street last week. 
   
   The person, Farabi Shafiur Rahman, had called for Avijit Roy's death in numerous Facebook posts, according to Roy's parents. 
   
   And within minutes after the Thursday attack, Rahman posted photos of the crime scene, said Col. Ziaul Ahsan of Bangladesh's elite anti-crime unit, the Rapid Action Battalion. 
   
   In a Facebook comment last year, Rahman allegedly wrote, "Avijit Roy lives in America. So it's not possible to kill him now. But when he returns home, he will be killed then." 
   
   In an earlier post, the same person wrote, "It's a Bengali Muslims holy duty to kill Avijit." 
   
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target: – The top suspect in the brutal killing of a Bangladeshi-American blogger has been apprehended, Reuters reports. Farabi Shafiur Rahman, who was arrested at a bus stop in Dhaka, Bangladesh, has confessed to threatening blogger Avijit Roy, officials say. "It's a holy duty of Bangalee Muslims to kill Avijit," he wrote on Facebook last year, according to police. Farabi was jailed in the past in connection with an Islamic extremist organization; Roy battled extremism in his writings. Farabi was also arrested last year over social media comments backing another blogger's death, though he was released in that case. That blogger, Ahmed Rajib Haider, was similarly hacked to death, CNN reports.