we're calling the person who returned stolen notebooks a "benefactor"?
What else should we call them? All we know right now is that someone returned them. We don't know if that's the same person who stole them. Personally I am hoping for someone to come forth with a story. At that point we can re-evaluate the use of "benefactor."
...or even that they were stolen. They could have been taken out legitimately and the paperwork was messed up in some way. The person who borrowed them may have died.