A member of the United People's Democratic Front (UPDF) was detained by the Bangladesh Army from the Kharikhyong area in Naniarchar upazila of Rangamati early Friday.
The detainee was identified as Prashanta Tanchangya, 52, an active member of UPDF.
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Lt Col Rubaiyat Hussain PSC, commander of Naniarchar Zone, said they nabbed Prashanta conducting a drive at Guichari in the Kharikhyong area in the early hours of Friday.
During the drive, a pistol, two rounds of ammunition, a walkie-talkie, four notebooks and a copy of the extortion money receipt were seized from his possession.
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Prashanta has been involved in extortion and murder, said the official.
He was later handed over to the Rangamati police station.
Legal steps are underway against the detainee, said Md Kabir Hossain, officer-in-charge of Kotwali police station in Rangamati.