Pre-employment background checks have become a standard practice in most industries, and for good reason - they allow employers to ensure their prospective employee is qualified, honest, safe, and responsible. For some positions, though, a single background check performed during the initial hiring may not be sufficient.
Childcare providers, for instance, are often required to pass annual background checks in order to continue working with children (for obvious safety reasons). A daycare worker may have a "clean" record today, but in six months the same individual could have been arrested, charged, and convicted of a sexual or violent crime - offenses unbefitting of their position. Without recurring background checks, it's possible the employer could remain completely unaware of the transgression, putting young lives and the business' reputation at stake (not to mention the potential legal ramifications).
Unless your employee (or another source) informs you of their run-in with the law, how would you know? Of course, unexcused absences due to incarceration may indicate something has happened, but not all convictions result in jail time.
Believe it or not, even time served can be hidden from an employer. Individuals have been known to take extended vacations or sick days to account for their absence and there are even programs to help inmates juggle their incarceration with a full time job, such as Weekend Jail.
Weekend Jail allows individuals to "check in" on Friday evening and "check out" on Sunday night, just in time to rest up and report back to work on Monday morning. Time is served in small increments and employers can be left none the wiser.