Import purchase and making sales for interstate

Dear All,

I have a question related to interstate sales of imported goods. Our Firm X is in Palanjur, Tamilnadu (which is exempted from tax) is importing goods which are cleared at West Bengal Port. We have to make a sale of the goods to a Firm Y in Guwahati, Assam. I have the following question: Can Firm X claim purchase in Tamilnadu and send the goods directly to Guwahati with dcouments (Invoice, DC, JJ Form) , and make a sale to Firm Y in Guwahati without the goods entering Tamilnadu?  Does this kind of sale have to be e supported with Form E1 or E2? Kindly help me out .  

But, the main point is that the Invoice has to be raised by Firm X only to Guwahati customer.

Regards