Deputies were called to Oliver's Ace Hardware on the 4000 block of San Pablo Road around 9 a.m. today on a report of a robbery in progress, sheriff's office spokesman Jimmy Lee said.
They found the victim, a 49-year-old man whose identity has not yet been released, in the parking lot with stabbing wounds to his upper body, Lee said.
He was taken to John Muir Medical Center, when he was pronounced dead shortly after 11 a.m.
Deputies searched the area and arrested Hercules resident Daymond Agnew, 34, inside a nearby home. He was booked into Contra Costa County jail this afternoon on suspicion of murder, and is being held in lieu of $1 million bail, Lee said.
The motive in the attack remains under investigation.