My father is applying for a US visa for the first time. In the interview process he was asked to bring his old passport too, which unfortunately he had destroyed after it expired many years ago. He never travelled outside India on this old passport. Does he need to bring some kind of document proving that he had an old passport and had no visa on it? Any help would be appreciated. Thanks!
Some Indian passports mention the number of the previous passport; if your father's does, he needs to keep that referenced passport with the present one ALWAYS. Under no circumstance are you supposed to throw it away. If the previous passport number is mentioned but you don't have that passport, a FIR copy will be required from the local police station mentioning all the details of how the passport went missing.
If your father's present passport doesn't mention the number of the previous passport (on the last page), you don't need to tell them that he had one.
And for future reference: Never throw away a passport. Even an expired or cancelled one.
Although the instructions mention that you should bring all previous passports to the visa interview, they may not necessarily ask to see them. In all US visa interviews I have attended so far, I was never asked to show my old passports.
As far as your father's visa application is concerned, I don't think not having his old passport is a big issue. In case they ask to see the old passport (which is very unlikely) - just state the true facts.
However, as a general guideline, NEVER destroy an expired/cancelled passport. The passport office returns your cancelled passport to you for a reason. You are supposed to keep it with you.