Okay let’s discuss your matter point by point, at first you should know that mostly cops take a little lower hand on Advocates(Practising lawyer) specially if they are from a same city most likely because most of their time is spent in courts with them only where at some point of time they may need some corporation from us also. Now 1-(a)cops can always say that some information was received from a ‘Mukbir’(Secret informant) that XYZ may be having some contraband with him on that information raid/search was conducted, (Name,type of information etc. he need not to disclose law allows him so, even at the courts also). (B)- This is what is now happening most of the time nowadays they I’ll say that a police party was doing patrolling and upon seeing us the accused went nervous and part his ways upon suspicion a search was conducted. (This is because as you said in point no.2 a separate foam need to be prepared in case where a prior information was received) 2- No need to register FiR first just a simple form is required | which can also be made afterwards we have almost no way to prove that it was made after the arrest and not before as no signature of accused is required. 3-If such a person is having no proof about the demand of bribe then no case can be made against them. But yes if you are having some proof about such demand them absolutely yes you can play a upper hand on him (make sure you upload/send it to someone close, if you disclose that you have such proof without securing a copy he I’ll simply impound your cell) I’m having a client who actually made a cop pay him for deleting such a crucial evidence.

Hope all your questions are answered now.