Insetad of jumping from tree to tree like a circus monkey why not ask for trial at international court of justice instead of Pak? is India that helpless or is it afraid that what ever witness you have will spill the beans...
As for going to ICJ .... when Pakistan is "cooperating" what is the need to go anywhere ... they have already arrested something like 120 people arrested in connection with "investigations" ... so as long India is able to "prod" Pakistan into action with active involvement of international community, i see no reason to go to ICJ (i dont think it would be under their jurisdication anyway)