Why don't you look up the cascius coins' address on a block explorer site and see whether it still has funds in it or not? See if those addresses are in your USB wallet.

If all the money has been sent from the address then see if the destination address is in your electrum wallet (this would be a private key sweeping transaction).

Block explorer would be a site like blockchain.info

Finally there is one last thing you can try but you have to do this offline. Open the site bitaddress.org and disconnect from the net. Go to wallet details tab and enter your cascius coin private key(s) there. For each private key you should get two addresses one for the compressed public key and one for uncompressed public key. Save those addresses in a text file for future reference. See if any of those addresses are in your electrum wallet.

Before going online again close the bitaddress.org tab and then your browser. You can run your browser once you've gone online again.

Alternatively you can do all of the above using a live cd. Bitaddress.org is just one self-contained file and can be saved on a disk for offline usage.