While a firestorm of protest and condemnation continues over the knife attack on Prof Muhammed Zafar Iqbal, a section of people are carrying out a virulent hate campaign against him on the social media.

Some of them in Facebook posts are even justifying the attack, branding him an "atheist" and "enemy of Islam". Some have hailed the stabbing and wished his death in comment sections of news portals.

Legal experts say these remarks are instigation of criminal offences and punishable under the existing laws.

But records of arrest for hate campaigns in online platforms are hard to come by. Instead, in many cases, police arrested bloggers and freethinkers for their posts that law enforcers believed “hurt people's religious sentiment”.

Police actions were really prompt when it came to anti-government writings online.

However, a top official of cyber security division of DMP said they have been working to track down those writing such posts against Prof Iqbal.

Prof Iqbal, a faculty member of Computer Science and Engineering department at Shahjalal University of Science and Technology (SUST), was stabbed on the campus around 5:30pm on Saturday. He suffered injuries in the back of his head, one in his back and another in the left hand.

Foyzur Rahman, a youth aged about 25, who was caught red-handed after he attacked Prof Iqbal, told the Rapid Action Battalion that he considered Prof Iqbal an “enemy of Islam”, officials said.

Revered by students of any age across the country, Prof Iqbal is popular among kids especially for his science fiction novels. All his life he has been vocal against communal forces and championing secularism and the ideals of the Liberation War.

Prime Minister Sheikh Hasina led the nation to condemn the attack and directed the law enforcers to hunt down all the culprits involved.

People from all walks of life, including eminent citizens, teachers and students of SUST and other universities and members of socio-political and cultural organisations, joined demonstrations on the streets as well as the chorus of protests on social media.

But there are people who are running smear campaigns -- some of them appearing to be supportive of extremist views. Foyzur, the alleged attacker, is also a follower of Salafism, an ultra-conservative reform branch within Sunni Islam, according to some locals in his home village in Sunamganj.

"Didn't he die?" questioned a Facebook user named Jajabor Amin in the comment section of a news item soon after the attack. Just below, another user, Shakil Hamja, wrote: "Good news! Atheist!"

One Rakibul Hasan in a post used abusive language against Prof Iqbal and said, "Zafar Iqbal is a person who is extremely anti-Islam..."

Abdul Kader, another user, justified killing of atheists, and said, "Those who are blaming Zafar sir's attacker please think again."

One Md Kamruzzaman Ripon commented, "He [Prof Iqbal] is a hardcore atheist! Either the knife that man [the attacker] used for the attack was not sharp enough or the atheist was too strong to die."

JD Khan, another user, in Facebook praised the attacker and said, “I demand awards be conferred upon him."

However, some netizens have demanded action against those involved in the hate campaign.

"Those who are supporting the attack on public domain should be hunted down.... Govt [Government] is doing nothing, so these animals write whatever they want,” one of then wrote.

Condemning such campaigns, Bangladesh Islamic Foundation Director General Shamim Mohammad Afzal said Islam never supports this type of character assassination.

“You cannot label a person as atheist or anything like this. Only Allah will judge his/her action. Those who spread hatred are not followers of Islam in true sense.”

Those who are involved in such practices are actually creating anarchy in society, he told The Daily Star.

Supreme Court lawyer Jyotirmoy Barua said freedom of expression and incitement to commit crime is not the same thing. "Such comments are manifestation of criminal minds and clear incitement to commit criminal offence."

He said if some of these instigators are arrested, others will get a message that it is a punishable offence. Unfortunately, instance of arrest of such people is very rare, he told this correspondent.

Contacted, Alimuzzaman, deputy commissioner of social media monitoring and cyber security division at Dhaka Metropolitan Police, said such posts drew their attention.

"We are working on this issue and trying to find out the people giving such posts and making those comments," he told this newspaper.