Suing an airline >

My parents flied Cathay Pacific and one of the luggage was opened, about $4,000 of stuff were missing. The perp knew which one to steal > internal job.
Airline wants to pay $410 for reimbursement, demands receipts for more.
My parents do not have receipts.
I see 2 ways out. Accept this $410 or sue them at small claim court.

Any suggestion how to go about it?

DOT complaint first, may get recompense through that before its necessary to try and file suit, which may be difficult if your Contract of Carriage says something else.

https://www.transportation.gov/airconsumer/file-consumer-complaint

And international travel has some limits, which are governed by some sort of international convention.  I believe the limit is a little over $1000.

Also check to see if their flight was covered by travel insurance or credit card travel insurance.  That's why i always book flights with my best credit card for travel insurance, as airline baggage limits are antiquated and difficult to navigate.  Also airlines are notoriously difficult to sue.

And international travel has some limits, which are governed by some sort of international convention.  I believe the limit is a little over $1000.

Also check to see if their flight was covered by travel insurance or credit card travel insurance.  That's why i always book flights with my best credit card for travel insurance, as airline baggage limits are antiquated and difficult to navigate.  Also airlines are notoriously difficult to sue.

Yep.  My recollection is that once you go international, then you are screwed.  However, if you could somehow prove that the theft took place on US territory, then your protections greatly increase.  This is yet another reason I always purchase travel insurance when going abroad.

I know,they are a pain to deal with. I already filed DOT complain, I don't know if that helps.
The flight was from SFO-PNH. It's missing somewhere along the way, since my parents landed in PNH, they applied Warsaw Convention.
I am trying to see when Montreal Convention is applied. Did google search, but found nothing.

Here is their liability.

Notice of baggage liability limitations

Liability for loss, delay or damage to baggage is limited unless a higher value is declared in advance and additional charges are paid. Excess valuation may be declared on certain types of articles.

For many international journeys (including domestic portions of international journeys), the Warsaw Convention may apply with liability limits of 17 Special drawing rights per kilo for checked baggage and 332 Special drawing rights per passenger for unchecked baggage. In cases where the Montreal Convention applies to your journey, the applicable liability limit is 1,131 Special drawing rights per passenger for checked and unchecked baggage. (The value of Special drawing rights can fluctuate - please check current exchange rates, Link opens in a new window operated by external parties and may not conform to the same accessibility policies as Cathay Pacific.)

You may want to consider posting to a social media if others had experienced lost item for the said route.  Perhaps others can share what their experiences are so you can weight your options?