Customs SI Mohanraj and the others were arrested by Madurai Rural Police and 39.5 kg of silver was seized from them, they said.
Mohanraj had led the gang and robbed the merchant, Govindarajan, of 52 kg of silver bars at Andipatti Bungalow in the district on November 24.
The merchant had purchased the bars here and was on his way to Salem when the gang waylaid him and after grabbing the silver dropped him in a jungle area at Malaipatti.