RAB sources said when a team was patrolling in Gondamara village in the upazila early Wednesday, some miscreants suddenly opened fire on them, forcing them to fire back.
At one stage, Alam was caught in the line of fire and sustained bullet injuries while the other gang members managed to flee the scene.
The injured was later taken to a local hospital where physicians declared him dead.
RAB further claimed they recovered four firearms, three sharp weapons and 13 rounds of bullet from the spot.
Chattogram RAB assistant director (media) Nurul Absar said there are nine cases against Alamgir with different police stations of Chattogram including Banshkhali police station.