yaar if your dad is personally in pakistan. Then i think this problem can be solved but provided you have all the documents and his Identity card photocopy atleast. You cann still lauch an FIR even if you dont know who he really was. But its far better that you actually can identify the person with his ID. Then police will be able to search his data, his home address etc. and later if he exited pakistan using his passport or not since all passports are machine readable now.
Yaar if you father knows someone in army , get this person identified first and his family. and then go on for there. But if you do have an ID card of his then launch an FIR as soon as possible.
And please dont think you will get this money really quickly. I doubt this would be that easy. Its a long process and you need to be patient and above all really lucky.
So pray to Allah. I hope you get your money back.