Unregistered Sex Offender in Illinois

My question involves criminal law for the state of: Illinois

Facts:
An individual was convicted and sentenced after having a prolonged sexual relationship with their own offspring younger than 12 years old. (Tier III Offender)

The case was a "Closed Session Hearing" and I am told the case details are sealed.

After prison, the offender bought a house which just so happens to be less than one mile from 3 public elementary schools.
(Another fact that eludes me.)

The offender registered for five years, then stopped.

My first question: How is any of this legal?

My second question: Is it possible for the victim to request a copy of the court case files including police records pertaining to the crime?

My last question: What steps (if any) should I take to expose this offender?
(Their name can no longer be found on any Registry: State, County or National)

If you believe that a sex offender is living near you who is required to register but has failed to do so, notify the police of the situation. It's not an emergency, so I suggest calling a non-emergency number.

Assuming the offender was an adult, the court file would be a public record available (for a copying fee) at the courthouse. Police reports are not ordinarily included in court files; if it's not, the victim can contact the investigating police agency to find out if the report is available and their procedure for ordering a copy.