22-year-old Masud Rana, an operative of the Jamaatul Mujahideen Bangladesh (JMB), confessed he opened fire on Kunio Hoshi, Deputy Inspector General Rangpur Humayun Kabir said.
Kabir said Rana, a former student at a local Islamic seminary, confessed to Magistrate Shafiul Alam at a Rangpur court yesterday that he and his accomplices attacked Hoshi, 66, and killed him.
Five other men are held up in police custody over Kunio's death, but officers say they are still hunting for the mastermind behind the attack.
Apart from the murder of Kunio, police have found JMB link to the murder of a Khadem and an attack on a Rangpur Medical College Hospital staff, Kabir told reporters.
He, however, did not mention when the Kunio murder suspect was held, the DailyStar reported.
Prime Minister Sheikh Hasina's government has accused the main Opposition BNP and its Islamist ally of trying to trigger violence in the country. The parties reject the claims.
Bangladesh has been roiled by rising unrest: Four atheist bloggers and a publisher have been hacked to death this year.
In another attack, Rahamat Ali, 55, a khadem of a mazar, was hacked to death in Choita intersection area under the same upazila on November 11.
On November 9, three criminals shot and injured the personal assistant of Rangpur Medical College Hospital director at the city's Ideal intersection on his way to his office.
