The incident happened at an Aldi store at 2906 Laporte Ave. in Valparaiso at 7:20 p.m. Friday, police said.
Thomas Powell, 36, of Hebron, Ind. walked into the store wearing a mask on his face and demanded cash, police said. Powell inferred he had a weapon in his pocket while demanding the money, police said.
He did get some money, but as he tried to run away, five to six customers held him down until police showed up.
Powell was arrested and held on robbery charges. No one was hurt and all the money was recovered at the scene, police said.
Those restraining him included a cardiologist and the owner of a local restaurant, witnesses said on Facebook.
If they were, police want to speak with them.
"If you assisted with the apprehension of the subject in the store on Friday evening, police would like to thank you and speak with you," a statement on Valparaiso Police Department Facebook page said.
"Individuals involved were witnesses to the robbery and police would like an explanation of the incident from as many witnesses as possible," police said.
They especially want to talk to anyone who is in the photo the department has released. Witnesses should call Det. Tom Horn at (219) 462-2135.
The Sun-Times Media Wire contributed to this report.