CBCID had taken in Syed Abu Dahir, running a footwear and textile shop in Ukkadam area for questioning late last night, police said.
As the news spread, PFI activists gathered in front of the Commissionerate to know the reason behind his being taken into custody, they said.
They dispersed later after Commissioner A Amalraj told a delegation which met him with a petition that CB-CID might have taken him for questioning and he would inquire into it.
Police have yet to make a breakthrough in the case.
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