A video of the lynching went viral on social media
Three people were detained during joint raids in Haramia and Sener Haat areas of the Upazila on Monday.
The raid started around 6am and was still on in the afternoon.
RAB’s media wing Assistant Director Maksudul Alam said at least 19 firearms were seized.
They include one AK-22 rifle, pistols, revolvers, different kinds of guns and ammunition.
Commander of RAB-7, based in Chittagong, Lt Col Miftah Uddin around told bdnews24.com: “The raid is being conducted based on a tip-off. The drive to recover the arms is still on.”
RAB officials said the media would be briefed later on the details and the detainees.
The elite force suspects those held may have links with acts of piracy and kidnappings in the island Upazila.