An e-mail, sent to the media from email@example.com, claimed credit some four hours after the killing on Friday.
In the past, a purported Twitter account of AQIS claimed responsibilities for the killings of bloggers Avijit Roy and Ananta Bijoy Das.
Niloy, who wrote against communalism and fundamentalism, was hacked to death at his house in front of his wife after Juma prayers by several youths.
He was killed in the same way like other bloggers, said detective police’s Joint Commissioner Krishnapada Roy.
One Mufti Abdullah Ashraf, who claimed to be Ansar Al Islam spokesperson, was the sender of the e-mail.
The e-mail said the AQIS carried out the killing and threatened more such attacks.
But police say they have no information about AQIS or al-Qaeda’s involvement in the killing.
Home Minister Asaduzzaman Khan Kamal told bdnews24.com he learnt about the matter from this correspondent.
He said he would discuss it with relevant authorities and ask them to seriously look into it.