His father Ajay Roy, a noted physicist, filed a case of murder with Shahbagh police on Friday .
Shahbagh police Sub-Inspector (SI) Sohel Rana said the case did not name anyone and was filed against unidentified assailants.
“Extremists are behind my son’s murder and Jamaat (-e-Islami) has backed them,” Ajay Roy told journalists after filing the case.
He also hoped that the government will bring the murderers to justice.
A bio-engineer and a naturalised US citizen, writer Avijit Roy was hacked to death near the TSC intersection at Dhaka University on Thursday.
His wife and fellow blogger Rafida Ahmed Banna was seriously injured as she tried to defend Avijit.
Religious radicals have been threatening Avijit for his active campaign against Islamist extremism.
He was a regular bdnews24.com columnist and the founder of the popular blog, Mukto-mona.
That was barely 10 days after the secular platform Ganajagaran Mancha started its Shahbagh-based agitation, demanding capital punishment for war criminals and a ban on communal parties like the Jamaat-e-Islami.
Islamist radicals had attacked other secular bloggers like Ashraful Alam and Asif Mohiuddin after the Shahbagh agitation polarised opinions in Bangladesh.
Islamist blogger Farabi Shafiur Rahman had allegedly threatened Avijit Roy with death once he returned home.
A screenshot of a Feb 9 post on Farabi’s Facebook timeline is still circulating on the Internet.
In that post , he is seen telling one Mannan Rahi that Avijit Roy cannot be killed now since he is in US, but he will be killed once he is back to Bangladesh.
Farabi has also been demanding that Rokomari.com, an online shopping portal, stop selling Avijit Roy's books.
Police had arrested Farabi in connection with Rajib Haider’s murder on charges of incitement, but he managed to secure bail .