A group named 'Ansar al Islam Bangladesh-2' has claimed responsibility for the killing of Rajshahi University teacher AKM Shafiul Islam.
The sociology teacher was struck with sharp weapons by several youths in front of Bihashpalli when he was on his way home on Saturday afternoon.
He suffered grave injuries on his head and shoulder, and died at the Rajshahi Medical College and Hospital.
The group's Facebook page, which was opened around five hours after the murder, says: "Our Mujahideens (fighters) executed a 'Murtad' (apostate) today in Rajshahi who had prohibited female students in his department to wear 'Burka' (veil)."
The page shows a picture of the slain teacher with a red X-mark on it. Below it is written in Bangla: "AKM Shafiul Islam (file closed)/ Offence: Apr, 2010/ Punishment: Nov, 2014."
It follows with an English statement: "We don't forget. Insha'Allah we will not forget others."
The group's Facebook page also names who these 'others' are. The page carries the photographs of five people.
Three of them are those of RU teacher Islam, murdered blogger Rajib Haider, and one Ashraful Islam. They are marked with red 'X' marks, and captioned: 'finished'.
The other two pictures are of bloggers Asif Mohiuddin and Rakib Mamun. The caption for them says: "First attempt: completed; second attempt: coming soon."
The page also issues a threat, reading: "Beware all the Islam opposing atheists-apostate!!!".
The few posts in it quote reports by a Bengali newspaper, 'Doinik Sangram', known to be the mouthpiece of Jamaat-e-Islami.
One of the posts reads: "Professor Shafiul Islam, while being the chair of the sociology department, recruited teachers on condition of being clean-shaved and not wearing kurta-pajamas. He barred female students from wearing burka in classes. This led to many students abandoning burka against their will."
Ansar al-Islam, an Islamist militant outfit, began operating in Iraq and Syria, where the 'Shariah'-based Islamic State is active.
Another Facebook page styled 'Ansar al-Islam' in Bangla found on the social media, was opened on Sep 9 this year.
Meanwhile, the Facebook page of 'Ansar al Islam Bangladesh-2' was opened around 8pm on Saturday.
RU teacher Islam, 48, was hacked around 3pm and was declared dead by the doctors an hour later.
Police say they were aware of the Facebook post claiming responsibility for the murder.
"We have noticed the post on Facebook. It's being looked in to," Matihar police OC Alamgir Hossain told bdnews24.com on Sunday.
Two persons have been detained from the Bihashpalli area after the murder, said the police officer, but he declined to reveal their identities.
Meanwhile, the Detective Branch (DB) of the Dhaka Metropolitan Police is yet to confirm whether Ansar al-Islam Bangladesh at all exists.
"We do not know of any organisation by this name. But new outfits are emerging now and then. So the existence of Ansar al-Islam Bangladesh cannot be ruled out," a DB deputy commissioner, working on militant outfits, told bdnews24.com on condition of anonymity.