"but Kinkos keeps no records of faxes"
Wouldn't it be on the phone bill for Kinko's?
All modern fax machines keep a fax log internal to the machine. There's some magic sequence of keys you press to print it out. If we had someone there, we could have them tell us the make/model of the fax and we could look up the key sequence. They just need to rent a computer and get on FR.
I still think the key is the log for the computer -- those memos were typed using default Word settings by someone who couldn't fake it well. Odds are they typed it quickly at Kinkos and then faxed it from there.
Occam's razor - the simpliest explaination is usually the correct explaination. If we find a familiar name on the sign-in sheet from the last two or so months, you have the scene of the crime.