ISI money to BNP leader!

This relates to BNP officials asking for proof about ISI (Pak) giving money to their leader! The matter has come up in the judicial inquiry going on in Pakistan about political and military related matters there.
It was published in their dailies and then most dailies in Bangladesh published this in the last few days. So the matter is not totally baseless; or 'a pie in the shy' as the saying goes!
If the BNP leader is guilt-free, then she should take up the matter judicially. And since it involves transnational issues, why doesn't she sue the Pakistan ISI in the International Court of Law? That will be legal and logical; instead of just making hue and cry about it; as it is now public knowledge! Why does not the BNP leadership take up this matter in the proper legal and logical way? Or is BNP incapable and not fully sure of the matter themselves; then it will remain a popular barb against them; come next general election!