How to prosecute an impersonator

You can complain to his higher authorities on his transgression of authority. There is no way you can initiate any criminal action as he is not impersonating anyone. At the most, he would be reprimanded for signing such applications if it is beyond his powers. 

on what ground you would complaint to higher authorities without any valid proof may be he is signed as ddo in the applications but do you have any valid proof that he is taking amounts from cuistomers

in my view first gather irregularities in the application where he signed and those application are not up the standards to give loans basing on that you can give complain to higher authorities that he is not taking proper care while granting loans which leads to failure to pay loans from customers and loss to government

You are not able to describe facts in straight manner.

(i) who committed fraud?
(ii) how committed fraud?
(iii)what document he signed?
(iv) for whom he signed?
(v) how the documents were false?
(vi) to whom he submitted documents?
(vii) what benefit he derived out of the transaction?
(viii) what harm you faced out of the transaction?

Apart from above ambiguities, you have conveyed that it is a loan matter from Govt bank.

(i) loan is for how much amount?
(ii) in whose name?
(iii) for what purpose one was taken
(iv) actually taken by whom?
(v)How amount delivered to imposter?
(vi) Did the bank not verify the identity of the actual applicant.

repeated

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