The killing happened at Johnny's Food Market on Maryland Avenue in Wilmington around 6:53 p.m.
Police say there were at least 8 people in the store, including customers and the victim's family, when two men rushed in and demanded money.
During the robbery, the owner was shot in the head and killed. Police have not officially released the man's name pending notification of family.
Investigators are checking to see if surveillance cameras were recording.
"This to me is pathetic that there wasn't some type of surveillance. There have been robberies and shootings and killings in this neighborhood. We have to live here, there has to be more protection for us," Wilmington resident Yvette Pelt said.
Johnny's Food Market is an institution in Wilmington and has been around for decades. The victim took over the store about 10 years ago.
"He was very good to the community. He gave them credit, if people don't have anything to eat, he greets you nice," resident Deborah Gilmore said.
Councilman Kevin F. Kelley Sr. who represents the area says he's confident the killers will be found.
"Unfortunately, we've become a city where people want to continue to rob people for their money or household possessions and we're going to win the battle at the end of the day," Kelley said.
But in that battle, Yvette Pelt wonders how many more innocent lives will be taken.
"The man was just gentle, he was a kind soul and he will not be forgotten in this neighborhood," Pelt said.
Police had only a vague description of the suspects.
Anyone with information is asked to contact Detective Scott Chaffin at (302) 576-3628, Delaware Crime Stoppers at 1-800-TIP-3333 or online at www.tipsubmit.com.