Whose money is lost ? and who has to complain ? Who is the culprit ?
If it is a forgery, the complainant should file complain first to the Bank branch denying the signature as there is gross negligence and such payment of forged cheque is not in due course.
If the cheque is established as forged, the bank has to immediately credit that amount to the depositor and as they have lost their own money, they should complain against the collecting bank and it's customer. If the cheque is crossed no one can find fault with collecting banker as they have done the credit after realization in good faith and without negligence that their depositor credited that cheque received in a bonafide manner.
The collecting banker must recover that money as an obligation towards a fellow banker from their customer.
This is the normal procedure. The police taking up the case is not known or proper. Anyway there is nothing to be disturbed as I told you that how the cheque was parted from the custody of drawer is more important.