Police Chief Michael O'Connell says its unclear if the SUV is linked to the crime.
Investigators are working to enhance the image further in hopes of clarifying the make, model and license plate.
On February 2, a gunman killed five women during an apparent robbery attempt at the store. A sixth woman survived the shootings.
A $60,000 reward is being offered for information leading to an arrest. Anyone with information should call Tinley Park police.