Once a sex offender is convicted, he/she is required by law to register with the local police. The police enter the information into a national sex offender registry. The purpose of the registry is to help local citizens know when a sex offender moves into their neighborhood. Anyone can access the registry to see if offenders live in their area.
What Megan's parents weren't aware of at the time, was that three convicted sex offenders lived within walking distance of their home. Police questioned the three. Two had solid alibies.