assuming that the sex offender has actually been
a convicted sex offender. If yes, than it's most
likely that the facts of his case are public record.
You can go to your local court house and search
these files. It's actually surprising how much
is public information. Plus, if your state enforces
Megan's Law, then he is required to be identified
in your community as a sex offender. Sadly, there
are probably other sex offenders in your area
who haven't been convicted and these are a greater
worry -- since they have no one watching them.