IG ATS Aseem Arun said the Kanpur unit of the ATS was tipped off that an arms dealer in the city was conniving with some people in Bihar and selling large number of arms using fake licences and a case was was filed in this connection in May.
Later, four persons were arrested in Kanpur and their interrogation revealed that the arms were being sold to Upendra Singh and others from Munger, the IG said.
Singh told the police that after purchasing arms they used to sell them to criminals and suspected Naxals at high rates.
The IG said Singh's interrogation was going on.