Most landlords don't run any sort of criminal background check (which costs money) - and don't typically look to see if their tenants are registered sex offenders, unless they have some overwhelming reason to suspect such, AND are willing to pay for it. They look at a credit history and if they feel they can pay, the tenant is in. The onus for remaining within the law of where they can live or not is up to the offender (kinda stupid, huh?). You being able to find out for yourself that someone is a registered sex offender is the whole point of the online systems. You can of course make this information known to the landlord (as well as other tenants), but if the guy is paying his rent on time, not causing problems, and not living in some area that is restricted due to sex offender status, things will likely remain status quo.