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JOLIET, Ill. — A special prosecutor will take over the case against a Joliet police officer who is facing charges in a fatal crash that left a Berwyn police officer dead over the weekend, officials said Monday.

Illinois State Police initially issued a misdemeanor ticket to 35-year-old Joliet Police Officer Erin Zilka after the Dodge Durango she was driving crashed Sunday morning, resulting in the death of her passenger, 33-year-old Berwyn Police Officer Charles Schauer. Both were off-duty at the time.

While the ISP recommended Zilka be charged with driving under the influence and driving too fast for conditions as well, the Will County State’s Attorney’s Office said Monday those charges have yet to be formally filed because the office is conducting a “thorough investigation.”

Zilka’s attorney Jeffrey Tomczak said Monday that her blood alcohol content was under the legal limit, according to blood tests that were taken within an hour of the crash.

And while the ISP is the lead investigative agency on the case, the Joliet Police Department said Monday it is also conducting an internal investigation into Zilka.

If any additional charges are filed, a special prosecutor will be appointed to handle them. Citing a potential conflict of interest, Will County State’s Attorney Jim Glasgow asked to have his office removed from the case Monday, and a judge approved the motion.

“We were summoned into the chief judge’s office at the request of the Will County State’s Attorney’s Office and they have filed a motion for the appointment of a special prosecutor,” Tomczak said. “They have asked to be removed from the case and the chief judge did grant that motion.”

As the state’s attorney continues their investigation, Zilka’s attorney is calling on the ISP to interview witnesses who they say could testify to the conditions on the road at the time of the crash, saying they would underscore there was nothing she could have done to avoid the impact.

Just after 6 a.m. Sunday, Zilka crashed into the rear of a Hino box truck that stopped in one of the right lanes of I-55 near Plainfield after it was involved in a crash. A 42-year-old Plainfield man has since been charged with driving under the influence, among other charges, in that initial crash.