In a video circulated online, the leader of Al Qaeda in the Indian subcontinent said its operatives hacked Avijit Roy to death with a butcher knife in February, according to the SITE Intelligence Group, which monitors militant groups online. The secularist blogger was with his wife when he was attacked in a Dhaka street.
Dhaka Metropolitan Police detectives, however, said Monday that they believe a local radical group, the Ansarullah Bangla Team, was behind the blogger's death, possibly with the help of Al Qaeda training.
Ansarullah Bangla has also claimed responsibility for Roy's death, using a Twitter account that police have not been able to verify as genuine.
Police spokesman Monirul Islam said investigators are looking into whether Ansarullah Bangla members received training from Al Qaeda.
"We have information that several militant outfits in Bangladesh follow Al Qaeda," he said.
Al Qaeda leader Ayman Zawahiri announced in September that the organization was expanding into the Indian subcontinent "to raise the flag of jihad" and bring Islamic rule to the region. However, there had been no activities previously linked to the new branch.
Bangladesh is an overwhelmingly Muslim country whose legal system is partially based on Islamic law but which is governed as a parliamentary democracy.
In the video attributed to Al Qaeda, which circulated online over the weekend, AQIS leader Asim Umar said his followers were responsible for several recent killings of "blasphemers" in Bangladesh, Roy among them. The others included Rajshahi University professor Shafiul Islam and another blogger, Washiqur Rahman Babu.
Lt. Col. Abul Kalam Azad, director of the intelligence wing of Bangladesh's Rapid Action Battalion, a police anti-terrorism unit, said his force was unsure of the video's claims. "We first need to check from where and which link the video was uploaded and to see if it is a fake ID."
Roy, who was of Bangladeshi origin but lived in Atlanta, was an outspoken opponent of religious extremism. Police have arrested one man in his death, an extremist blogger named Shafiur Rahman Farabi, but he is charged with incitement, not wit taking part directly in the killing.
Islam, the police spokesman, said detectives have identified five other people linked to the killing "and are trying to arrest them."