Commander of the banned militant outfit Jama`atul Mujahideen Bangladesh (JMB) of Chittagong unit Mohammed Javed has been killed in a grenade explosion on Tuesday, a day after his arrest in Chittagong.Police arrested Javed and four other JMB men and recovered nine grenades, a pistol, 120 bullets, and bomb-making materials during raids in the port city yesterday evening.Following the information obtained from the arrestees, a team of detectives conducted a drive with Javed in Oxygen area of the city around 4:45am to recover more firearms and ammunition, the police official said.