(CBS) — It’s a crime that shocked the south suburb of Flossmoor: a home invasion and sexual assault.

CBS 2’s Dana Kozlov has more on the investigation and why police believe the suspect left the area.

Homewood-Flossmoor police are now working with the Illinois Department of Corrections and the FBI in hopes of tracking down the attacker. That assumes he is an ex-offender.

The assault happened early Sunday morning in the 1200 block of Douglas in the south suburb. The victim was home alone at the time and told police he had what looked like a kitchen knife. The intruder was wearing a ski mask.

After the assault, he walked out the victim’s front door. Police believe he quickly left the suburb and they don’t believe he lives there.

Mary and Tony Chang have lived in this Homewood-Flossmoor neighborhood for 25 years. The attack has unnerved them.

Flossmoor’s deputy police chief, Tod Kamleiter, says his department awaits evidence results from the crime lab.

Police believe the attacker’s original motive was burglary.

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