Potentially stolen cards

Baez578

It appears that a package of two Roberto Clemente cards I purchased off a CU member are lost or stolen by the USPS in my town. I already submitted a complaint to the USPS postal inspectors thanks to the advice of some of you here.

My question now is.... Can I lock these cards with PSA as lost/stolen if both the seller and myself consent to the transaction?

I have it in my registry now but was curious if there's more I can do.

Thanks