The Detective Branch (DB) on Tuesday interrogated Buet teacher Farseem Mannan Mohammedy in connection with the killing of Bangladesh-origin US citizen writer-blogger Avijit Roy.
Farseem was grilled for nearly three hours at the DB headquarters on Minto Road on Tuesday.
"We called him (Farseem) for questioning. We wanted to know whether he had any personal dispute with Avijit regarding his writings or opinion," Monirul Islam, Dhaka Metropolitan Police Joint Commissioner (media), told the Daily Observer.
Avijit's father Prof Ajay Roy had earlier said the Buet teacher was involved in the murder.
According to Ajay, Farseem organised a meeting, which was attended by Avijit and his wife Rafida Ahmed Bonya, at Bangla Academy before the gruesome killing carried out on the Dhaka University campus on February 26.
Investigators say they are still clueless about the killers of Avijit, who was attacked by unknown assailants while coming out of the Amar Ekushey Book Fair with Bonya that day. She was also critically injured.
After the murder, police arrested only Shafiur Rahman Farabi, who had issued at least a dozen death threats to Avijit for what he said demeaning Islam.
Investigators also suspect that Redwanul Azad Rana, accused in the murder of blogger Ahmed Rajib Haider, is also involved in the killing of Avijit. Rana has been "missing" since February 26.
DMP official Monirul said they were trying to identify and arrest the attackers.
After Avijit was killed, Ansar Bangla 7, presumed to be an organisation of militants, celebrated the murder in a tweet and claimed responsibility for it.