Ripped off
What do you need from him that you don't already have? From reading USPS claims it appears they are asking for nothing at this point that he would have.
"If you received something damaged or items are missing from a package, please retain the contents you received and all the associated packing materials until your claim is settled. You may be asked to take them to your local Post Office™ for inspection later. Please do not reship the package."
https://www.usps.com/ship/file-domestic-claims.htm
File Domestic Claims
Most of the 700 million pieces of mail we handle every year arrive safely, but when things don’t go as planned we want to get any issues resolved quickly. For the best turnaround time, be sure to file your domestic claim online and follow the instructions.
To get started with a domestic claim for a damaged, lost, or delayed shipment, sign into USPS.com or register for an account. Then, enter your item’s label (or tracking) number.
Not only will you be able to start your claim immediately, you’ll be able to check its status along the way.
File Online
What do you need to file a domestic claim?
1 - Label (or tracking) number found on your online label record, package label, Extra Service receipt, or sales slip.
Some article numbers are 22 alphanumeric characters beginning in a letter and ending in "US."
Example: 9205 5000 0000 0000 0000 00
If you don't see a number like that, look for a string of 20, 22, 26, 30, or 34 numbers.
2 - Proof of value, damage, replacement, or repair costs.
You’ll need to upload a .pdf or .jpeg of sales receipts or invoices.
If you received something damaged or items are missing from a package, please retain the contents you received and all the associated packing materials until your claim is settled. You may be asked to take them to your local Post Office™ for inspection later. Please do not reship the package.
3 - Evidence of insurance and proof of purchase
If purchased online, use your Click-N-Ship® transaction number or the auction number (i.e., from eBay®).
If you shipped your package from a Post Office location, find your sales receipt or other proof to show the item was sent with insurance or Priority Mail Express™.
What do you need from him that you don't already have? From reading USPS claims it appears they are asking for nothing at this point that he would have.
"If you received something damaged or items are missing from a package, please retain the contents you received and all the associated packing materials until your claim is settled. You may be asked to take them to your local Post Office™ for inspection later. Please do not reship the package."
https://www.usps.com/ship/file-domestic-claims.htm
File Domestic Claims
Most of the 700 million pieces of mail we handle every year arrive safely, but when things don’t go as planned we want to get any issues resolved quickly. For the best turnaround time, be sure to file your domestic claim online and follow the instructions.
To get started with a domestic claim for a damaged, lost, or delayed shipment, sign into USPS.com or register for an account. Then, enter your item’s label (or tracking) number.
Not only will you be able to start your claim immediately, you’ll be able to check its status along the way.
File Online
What do you need to file a domestic claim?
1 - Label (or tracking) number found on your online label record, package label, Extra Service receipt, or sales slip.
Some article numbers are 22 alphanumeric characters beginning in a letter and ending in "US."
Example: 9205 5000 0000 0000 0000 00
If you don't see a number like that, look for a string of 20, 22, 26, 30, or 34 numbers.
2 - Proof of value, damage, replacement, or repair costs.
You’ll need to upload a .pdf or .jpeg of sales receipts or invoices.
If you received something damaged or items are missing from a package, please retain the contents you received and all the associated packing materials until your claim is settled. You may be asked to take them to your local Post Office™ for inspection later. Please do not reship the package.
3 - Evidence of insurance and proof of purchase
If purchased online, use your Click-N-Ship® transaction number or the auction number (i.e., from eBay®).
If you shipped your package from a Post Office location, find your sales receipt or other proof to show the item was sent with insurance or Priority Mail Express™.