"A team of CID (criminal investigation department) arrested him as a suspect," M Rokonuddin, additional police commissioner of northeastern Sylhet, where Ananta Bijoy Das was hacked to death, told PTI.
He said photographer Idris Ali, who works for a national and a Sylhet daily, was remanded into police custody for seven days for interrogation on orders of a court there. Later, he was brought to the CID headquarters here under security.
"We are awaiting the suspect to reach here later this evening," he said.
33-year old Das, a banker by profession, was the latest of three secular bloggers hacked to death this year by suspected Islamists after machete-wielding militants attacked him last month.
Also Read
In a related development, Bangladesh overnight banned Islamist outfit Ansarullah Bangla Team (ABT), suspecting its involvement in murders of several secular bloggers in recent months and over alleged links to al-Qaeda.
Police suspected the ABT to have sent the letters in the name of "Alkaida".
International security think-tank Terrorism Research & Analysis Consortium (TRAC) described ABT as an "al-Qaeda- inspired Islamic extremist group in Bangladesh that started its activities during 2007 as the Jama'atul Muslimin".
ABT is the sixth such Bangladesh-based outfits to be outlawed for militant and anti-state activities in the country, the rest being Hizb ut-Tahrir, Jama'atul Mujahideen Bangladesh (JMB), Harkat-ul Jihad Bangladesh (HuJi), Jagrata Muslim Janata of Bangladesh and Shahadat-e-al-Hikma.
Hours after the murder, a group called 'Ansar Al-Islam' claimed in a tweet that AQIS was responsible for Das's murder and warned that more such "atheists" awaited the identical fate.
Bangladesh earlier welcomed Federal Bureau of Investigation (FBI) assistance after Roy was murdered in Dhaka in February.