After such a traumatic experience like that i would not be lending keys either. You have already been burned once, and i would not be trusting after that and that's for sure. Your work colleagues have to understand that that is a serious offense that someone tried to blame you with that you could have been sent to jail for it! You could have lost your career, your liscence, your dignity. They should be understanding of your situation and realised you have learned the wisest lesson of all "COVER YOUR ASS!".