Officer Charles Schauer, 33, was a passenger in an SUV that slammed into the back of a box truck on I-55 near Plainfield.
The box truck had been involved in another crash shortly before the fatal incident.
Joliet police officer Erin Zilka was the driver and is facing a DUI charge, Illinois State Police said.
RELATED: Joliet Officer Erin Zilka charged with DUI in crash that killed off-duty Berwyn Officer Charles Schauer
Both officers were off-duty at the time.
Thursday, Will County prosecutors filed a motion to have a special prosecutor appointed in the case, citing a possible conflict of interest.
RELATED: Special prosecutor motion filed after Joliet Officer Erin Zilka charged with DUI in crash that killed off-duty Berwyn Officer Charles Schauer
Zilka is a 12-year veteran of the force. The Illinois State Police recommended that she be charged with DUI and driving too fast for conditions, but the investigation continues.
Illinois State Police said 42-year-old Rodrigo Marin of Plainfield was intoxicated and caused the initial crash with the box truck. According to state police, Marin lost control of his Nissan, crossed over the lane and struck the front left side of the box truck, which was in the right lane as it prepared to exit to Rte. 30.
Visitation for Schauer will be at Saint Vincent Ferrer Church, 1530 Jackson Avenue in River Forest from 4-8 p.m. Friday, followed by a funeral Mass beginning at 10 a.m. Saturday and internment at Queen of Heaven Cemetery, 1400 S. Wold Rd. in Hillside at 1 p.m.