Additional District and Sessions Judge Md Sultan Mahmud passed the verdict on Thursday.
The court also fined convict Tk 10,000 each, in default, to suffer three months more in jail.
The convicted were Mohammad Ali, son of Md Nur Mohammad of Relly Bagan village in Narayanganj sadar upazila, Md Sabbir Hossain son of Faruk, Md Sabuj Hossain son of Md Nur Hossain and Md Rabin son of Md Badsha Miah of Muslimabad village in Jamalpur sadar upazila.
According to the prosecution story, on August 28 in 2021 around 3am at night, some unidentified miscreants killed Arif, 28, on the bank of old Brahmaputra River in Hamidpur area under Jamalpur sadar upazila and took away his bike.
He was returning home in Machhimpur area by his motorcycle after parking his car at a garage in Nandina Bazar in Jamalpur sadar upazila.
Following a case, police arrested four people, including Mohammad Ali and Sabbir Hossain who gave confessional statement.