Kunio Hoshi, 65, was gunned down in October 2015 by masked men on a motorcycle on his way to visit a grass farm project in the northern district of Rangpur. The killing came less than a week after an Italian aid worker had been killed in a similar fashion in Dhaka's diplomatic quarter.
Public prosecutor Rathish Chandra Bhawmik said the five had conspired to kill Hoshi to destabilize the government and the country. Police said the accused were members of the banned militant outfit Jama'atul Mujahideen Bangladesh.
The court acquitted one defendant as charges against him could not be proved.