The teacher, Abul Kashem Badshah, 35, was gunned down on the first floor of the Kalabagan branch of the coaching centre on July 26.

The arrestees are Fahad Al Masud Ovi, 22, Sumon Hossain, 20, Saiful Islam Robin, 22, and Abu Bakar Abdullah Siddiq Rony, 23.

Acting on a tip-off, a Rab team raided a house at Charakghata in Hazaribagh at noon and arrested the four with a foreign revolver, seven bullets, Tk 98,000 and a motorbike. A sticker inscribed with 'Sangbadpatra' was attached to the number plate of the motorbike.

Masud told reporters at the Maghbazar office of Rab-2 that he, Rony and Sumon shot the teacher dead in the coaching centre.

He also said that Robin had a pistol in his hand but did not open fire.

Rab members said they have arrested Robin as they found the revolver used in killing Badshah and seven bullets from his possession.