Two men were murdered for Tk 18,000 they borrowed from their friend Md Tariqul Islam in Birganj upazila.
Superintendent of Police Syed Abu Sayem said this at a press briefing at his office in the town on Saturday.
During a primary interrogation, arrestee Tariqul, 27, son of Gias Uddin of Palpara village, confessed to killing the duo, said the SP, adding that Tariqul was held from Madonpur village on Thursday.
Deceased Biplob Chandra Roy, 23, owner of a computer shop at Kholakuti village, and Hanifur Rahman, 32, were good friends.
The deceased and the accused were drug peddlers and addicts, said the police official, adding that the arrestee was the cashier of their illegal drug trade.
On May 30, the throat-slit bodies of Biplob and Hanifur were found at Debipur Balapara village in the upazila.
Biplob and Hanifur borrowed Tk 18,000 from Tariqul a couple of months ago, but the duo did not return the money in time. Tariqul pressured them to return the money several times, but they did not pay it.
On May 29, the trio on the motorcycle of Hanifur went to Nilphamari, from where Tariqul purchased a knife.
The trio then purchased two bottles of Phensidyl and yaba pills from Dinajpur town and took the drugs, said the SP.
Later, they were heading towards Debipur Balapara village. Tariqul was the pillion passenger and Biplob was seating in the middle while Hanifur was driving the motorbike.
At one stage, Tariqul stabbed Biplob and Hanifur around 2:00am on May 30.
Police also seized the knife and motorcycle from the house of Tariqul on Thursday.