After FIR Police not arresting the main accused

Dear sir, I am on bail and the section under which I was arrested is 420,468,469.Here I would like to say that I was innocent and police arrested me.But there is same allegations on main co accused .After two month judicial custody now I am on bail.But after a gap of 5 month ,police is not interested to arrest main accused because SHO receives bribe on monthly basis,as I know. Here I would like to know that is there no time bound to arrest main accused.Where I should to approach so that main accused will be behind the bar.Please suggest.