The strong-arm robbery occurred at Travis Dairy, located at 140 E. Travis Blvd.
Three suspects assaulted and pepper sprayed storeowner Ho Jun Kim, 70, and stole items from the store, including the cash register, police said.
Kim called police at around 7:50 p.m. and reported that his store had been robbed and that he required an ambulance.
Kim was taken to the NorthBay Medical Center in Vacaville, where he died at 8:36 p.m., the Solano County coroner's office said.
Deputy Coroner Ray Lamb said he died of "cardiac arrhythmia due to emotional distress caused by an assault."
Detectives reviewed video footage from nearby businesses, interviewed witnesses, and recovered evidence including the cash register, police said.
Two 17-year-old boys and a 15-year-old boy from Fairfield and a 17-year-old boy from Vacaville were arrested and are facing charges of homicide and robbery. Their names are being withheld due to their ages.
Chelsea Johnson, 18, of Vacaville, was also arrested and is suspected of driving the getaway vehicle, according to police.
