So far, nothing is missing. We're thinking that the potential thief heard a signal trip (we have a system that alerts clerks to patrons wandering off to restricted areas) and that frightened him into leaving before he had time to take anything. What he didn't know is that we have a silent alarm that automatically called the police, so he was fortunate to hear the audible signal to the clerks, or he would be sitting in jail.

Seriously, what thief in his right mind would break into the library?