Hello,
Possibly. It depends how technical they are and if they changed connections, used an anonymous proxy while sending the prank email, etc.
The first thing to check is the
full email headers.
Compare the headers from an email really from your friend to one of the prank emails.
If they are using a free webmail service or the same ISP smtp server for both you may be able to catch them coming from the same IP address.
If you need any help with the headers please feel free to copy and paste them into a reply within this thread.

Welcome to Email Questions!
-Raymond