It could easily not be you,wait for the camera results,and they are just books,your boss is making too much of it.

I say just be straight up about it. Approach your boss and let her know of your thought process. These things have happened to us all before. If it sets you back from working the desk just think of it as a needed step to help you tighten up. If she begins to lecture just look at it as motivation to for you to perfect your skills. For every mistake there is an opportunity to learn from it.

My advice would be to go to your boss and explain exactly what you've said here, that you honestly thought it wasn't your mistake at the time, but that after looking into it later you realised it might have been. You don't need to admit it was you, just admit to the possibility, and say you're still not sure about it but you apologise anyway. Good luck.

Id just say I did it & discuss how to correct it & move forward. Im not sitting around waiting to be implicated. I might even blame them for poor training & a faulty system. lol

If the mistake was yours own it and try to be better next time it is all you can do

Sorry

In the big scheme of things... it was a mistake... no one is going to lose their life... it’s going to be taken care of... we all make mistakes. Learn and turn the page... [i]no pun intended [/i]

It is usually better to admit to a mistake voluntarily (and apologize sincerely) before being confronted by your supervisor.