Those detained are Binod Upadhaya of Kapilbastu municipality-1 and Satya Bijaya Chaube of Dhamauli-7, the police said.
The police also recovered Italian pistol with three rounds of bullets, home-made gun and rifle, one set of each.
They killed local businessman Ram Niwash Tiwari on December 11 and robbed 8.5 lakh from him, the police claimed.
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