Johnathon Kurth and five others died in the crash after his Honda Accord struck a tree. The car had been traveling 100 mph moments before the crash, police said Monday.
"Based on video, we know that people witnessed the shooting," Assistant Police Chief Jason Stille said. "And they need to come forward and give us the information that they have."
The man, wearing a medical mask, walked into the store near 10th Street and Lincoln Mall just after 1 a.m. Tuesday and demanded money, according to police.