Among the four, Maskawat Hasan alias Sakib alias Abdullah, JMB operational commander of Rajshahi region, was arrested from Gaibandha yesterday.
He confessed to his involvement with the killing, Rajshahi Metropolitan Police Commissioner Md Shamsuddin said at a press conference at RMP headquarters today.
The law enforcers arrested three other JMB men from Kharkhari area yesterday, the commissioner said. He however did not disclose their names, reports our district correspondent.
The trio aided the killers but did not take part in the killing directly, the RMP boss said.
The law enforcers seized a motorcycle used during the killing operation, and two sharp weapons from the possession of the arrestees, the commissioner said.
The law enforcers have so far arrested seven people in connection with the killing.
On April 23, Prof Siddiquee was hacked to death when he was waiting for the university bus in Shalbagan area of Rajshahi city.
His son Riyasat Imtiaz Shourav later filed a case with Boalia police station accusing unnamed people for the murder.
Police investigations found three youths, who went to the killing spot by a motorcycle, orchestrated the murder. They left the scene shouting “Allahu Akbar”.
Militant group Islamic State claimed responsibility for the attack, according to US-based SITE Intelligence Group, which monitors global terror activities.
The government maintains there is no IS presence in the country.