You cannot prove anything against them , because they actually didn't do anything against the law , They wanted to join mainstream politics but the state denied them .I am pretty sure he will be acquitted when he appeals in the higher court. As far as Mumbai attacks are concerned they will never do such an activity because this particular organization have no history of attacking civilians , you cannot believe the Indians they always lie. Also they only operated in Jammu and Kashmir .The legal standard isn't whether a group or individual conducts activities against the Pakistani State - the legal standard is whether money laundering occurred and/or material support was provided to proscribed organizations.
LeT/JuD/HS had all become liabilities for the State since the Mumbai attacks.
The State & national interests come first, everyone and everything else is dispensable.
Think about the game long term Stealth sahib.
That's all I'll say on this.