It's easy to change the 'from' address in an email to anything you like. Spammers do it all the time (and it's common for them to use the same address as in the 'to field, since the recipient's spam filters will see the address as a valid one).
In the list of messages, right-click on one of the spam ones and select 'Properties'. That will show you the path that the email took but it will only reveal the IP address of the spammer (or of the proxy that they've used). Using this website will tell you ISP and country but it won't tell you who the actual sender was. (Only the ISP can identify the sender)
http://whatismyipaddress.com/ip-lookup
(You need to replace your own IP address with the one found from 'Properties', above).
To be honest, I wouldn't worry about it. Everyone gets spam; while you can reduce it, it's almost impossible to block it completely.