"We will take the matter to the International Criminal Court and seek the trial of the members of the Pakistani occupation forces who committed crimes against humanity during our liberation war."However there is a problem with that because apparently the International Criminal Court came into being on 1 July 2002 — and it can only prosecute crimes committed on or after that date. (wikipedia)
I think Bangladesh can resort to the International Court of Justice which was established in Established in 1945 by the UN Charter. It may be noted here that the Nazi war crimes were trialed under the International Military tribunal established in 1945 by USA, UK, France and USSR. The tribunal came into being for the just and prompt trial and punishment of the major war criminals of the European Axis. So if Bangladesh establishes such a military tribunal with India and Pakistan then the proper justice of the genocide can be done easily.