Plainfield police said a car found frozen in Lily Cache Creek Monday had likely been there overnight.
Police got a 911 call around 7:10 a.m. from an employee at a Lily Cache Plaza business who spotted a gray Mercedes upside-down in the creek, just south of the bridge near Route 30 and I-55.
The vehicle was discovered with a deceased male victim, later identified as George C. Weathered of Joliet, still inside.
On Monday, Sgt. Mike Fisher said police were working to determine how long the car had been in the creek, saying the Mercedes was "completed frosted over" with ice when first responders arrived. Ice had also started to form in the creek, police said.
"I can tell you it was there for an extended amount of time," Fisher said at the time.
On Thursday, he said investigators now believe the vehicle wound up in the water sometime after 10 p.m. Sunday.
Read: Joliet Man Dies After Car Drives into Lily Cache Creek
"Our investigators talked to at least one family member who had spoken to him at 10 o'clock the previous night," Fisher said. No one had reported Weathered missing, police said.
According to the Will County Coroner's office, preliminary autopsy findings were inconclusive on Monday. Weathered's final manner and cause of death is pending autopsy, toxicological and police reports.
The Chicago Tribune reported that Weathered, 30, served 90 days in jail in 2008 after pleading guilty to attempted distribution of child pornography. Kane County prosecutors alleged that pornographic images of children were found on the then-25-year-old's computer. As part of his sentence, Weathered was required to register as a sex offender annually and was listed on the Illinois Department of Corrections sex offender registry.