Threat by mobile

There was threat about life given by mobile.It complaint lodge u/s 506,504 of IPC .complainant voice record of conversation with accused in mobile.but in chargesheet it not mention by IO.complainant also did not mention of voice recording in chief examination of court.but after complition of evidence stage.complainant file application for accept voice recording and examine in lab but trial reject it now it before session court. 1.what is solution for win complainant case 2.what is duty of IO in mobile threat case 3.which evidence IO should collect in thiThere was threat about life given by mobile.It complaint lodge u/s 506,504 of IPC .complainant voice record of conversation with accused in mobile.but in chargesheet it not mention by IO.complainant also did not mention of voice recording in chief examination of court.but after complition of evidence stage.complainant file application for accept voice recording and examine in lab but trial reject it now it befs case 4.Any judgement in favour of complainant