A foreign firearm, three rounds of ammunition, a magazine, and some drugs were recovered, said army sources.
Swapan admitted during interrogation to being associated with the UPDF since 2016.
Khagrachhari sadar police station sub-inspector Abu Hanif and sub-inspector Md Saleh Uddin said that Swapan was the chief collector of UPDF. He was held in a joint operation by army and police.
A case in this regard was being prepared, SI Abu Hanif said.