Which part of it do you want to dispute? That he was tortured to death? Or that it was done by pak army and not just mujahideens?
For the first question, there was the mutilated body handed over by pak to India. That's irrefutable proof, he didn't die from cancer.
Is it the second question? Then it would be impossible to prove, since pak army and govt have been in denial even about their involvement (and failure) in the war. You didn't even acknowledge that your soldiers took part in the war, and until 8 or 10 years later you didn't even put up an official list of the soldiers who died. You kept asking for "proof" of your soldiers involvement, after giving them a few nishan e haiders. So it is unlikely we would ever settle the question of whether it was your army or your mujahideen. But do such distinctions matter to Indians, do you think? As far as we are concerned, he was tortured and killed by Pakistanis. Mujahideen and soldiers are both from Pakistani society, a product of youir antion, both working together with the same goal. The only reason you call them "mujahideen" and refuse to call them soldiers is because your state wants plausible deniability, and want to make your society less guilty than it is. As I asked before, are people who call themselves "mujahideen" exempt from these codes of honor that humans have decided upon? Many PDFites are proud of your so called "mujahideens", who they think are fighting in some noble cause against India. If you agree with their existence, shouldn't you also hold them responsible for atrocities?