Sex offender lists and registries should not be the sole source used in a background check.
Many people have the same names and many people move. Positive identification is necessary in determining a person's criminal record. Many states require you to have permission from the subject that you are checking and many require that a fingerprint card be submitted in order to do a proper background check. Contact your local law enforcement for more information.

Each state has it's own guidelines regarding what sex crimes qualify for requiring a person to register as a sex offender. Not all sex offenders are required to register. Many states do not have a penalty for failure to register for those who are required to register. It also greatly depends on what the offender plead guilty to or was convicted of too. The person who broke into a home, stole some jewelry and raped a victim may have plead guilty to a robbery related crime and any rape charges were dismissed.

Some states do a very good job of collecting information from each city and county and adding it to one central state sex offender registry. Many states do not have a central registry so you would need to check local city and county records for sex offender information.

Not always. Many times an offender is only required to register as a sex offender for a certain length of time. If he does not re-offend and completes his sentencing requirements in that length of time, he may no longer be required to register as a sex offender.

Some states do notify residents that a sex offender is moving into the neighborhood while others do not. Many cities, counties and states require that you show proof of residency and require that you be a resident in the area where you would like sex offender information. There are often fees included as well and I've seen them ranging from $5.00 to $95.00. While it is informative to know where the sex offenders are in your neighborhood, it is more important that you have background checks done on anyone who provides services for you or your children. This can include caregivers, instructors, drivers or other domestic help. Anyone working with or around children should be required to have a background check.