Khulna police are interrogating the father and two friends of Saiful Islam, who was killed in an anti-terror operation in Dhaka a day ago.
Saiful's father Mohammad Abul Khair and friends Mohammad Sani, 22, and Isan, 21, were detained hours after the operation on Tuesday.
Khulna district police chief Mizanul Haque Mollah said they had questioned several people to learn more about Saiful.
Some were released after questioning but some others were still in police custody.
However, a former UP chairman claimed that the law enforcement officials had said they set Khair free after being asked by locals.
Police Superintendent Mizanul said they suspected Saiful was a member of Islami Chhatra Shibir, the student wing of Jamaat-e-Islami. But no evidence was found to support the claim.
Saiful’s sister Sabia Khatun claimed her brother was not involved in student politics. "He went to Dhaka looking for a job as he was struggling with his tuition fees," she said.
According to a local, Saiful's father was once suspended from the post of Imam at a local mosque because of his involvement with Jamaat.