Several agencies are involved with the investigation, including the Sandwich Police Department and Illinois State Police.
64-year-old Robert Wilson and his 85-year-old mother Patricia died five months ago from blunt force trauma after a forced entry into their home.
Officials believe the crime occurred between 7:45 p.m. and midnight Aug. 15; family members have been ruled out as suspects.
The Wilsons' stolen Chevy Impala was located near Lincoln Park Zoo in Chicago soon after, but DeKalb County’s Deputy Sheriff Andy Sullivan says surveillance video of the vehicle was unable to catch the driver’s face.
He says police are investigating leads, but he’s calling on the public to keep them coming.
“People may not have called in because maybe they thought we were already told something, but in fact, maybe we haven’t been told everything," he said. "So if somebody has information, we definitely want to talk to them. Nothing is too small.”
He says the investigation team will continue being persistent.
"We need to remain focused and vigilant, which we will. And we need to continue to develop these leads we have. And hopefully, one day, they’ll lead us in the right direction to a suspect,” he said.
He says investigators sent the state crime lab dozens of items for analysis, but doesn’t know how long results could take.
Police are offering a $25,000 reward for information leading to an arrest.
People can contact Crime Stoppers at (815) 895-3272 or at email@example.com.