Reinvestigation after Chargsheet

Hi I am having a query which I am posting below please advise me on same. My sister has committed suicide and her in laws were booked u/s 498, 306. However I have submitted several evidence against the accused persons to the concerned police station and police assured me that they will mention everything in chargsheet but however no witness statement and evidences were recorded in chargsheet. I have filed writ petition before high court for reinvestigation but for to annex the copy of charge sheet. Later I have taken out an application for ammendment in writ petition for exhibiting copy of charge sheet but however hon'ble Judge is not allowing the application on the ground that now trial has started and you face trial. My question is that whether any judgement/citation is there which allows the amendment in writ petition after filing of charge sheet. Help may be appreciated