CHICAGO (CBS) — Chicago police are seeking an unknown offender accused of kidnapping a woman and sexually assaulting her over the course of six days.

A 20-year-old woman was walking to a bus stop near the 6700 block of South Halsted Nov. 23 sometime between 5 p.m. and 6 p.m., police say. She was approached by an unknown man, driving a pickup truck, who punched her in the head and dragged her into the truck, according to police.

The offender is said to have then taken her to an unknown location and locked her in a basement room. Police say the woman was sexually assaulted multiple times by multiple people before she was released.

The woman told police she was blindfolded and dropped off at 69th and Lafayette.

The offender is described as an African American male, bald with a black beard and brown eyes, between 6′ and 6’2 of medium build around 40-45 years old.

He was last seen driving an older model, navy blue, four-door pickup truck with rust over the wheels.

Police ask anyone with information to contact detectives at 312-747-8271.