You are right that in case you lost any kind of certificates there should be an FIR or GD at your nearest Police Station. After that you need to submit your application to WBUT along with xerox of FIR or GD. But you should get in touch with your College Authorities a sin some cases like lost of Mark-sheet, just an application to WBUT through College is sufficient.
@admin in how many days/months we can expect to get our desired credentials??and how we have to deliver our application:-by post or we have to go to wbut office personally??in my case i dint lose anything,my college can't find,and on the top of that they can't even help me in that matter!!.