The man was found lying in a pool of blood near a pit toilet, said Captain Amanda Funani.
He had a gunshot wound to the head.
Police had spoken to the man’s brother, who had found the body.
Funani said his brother had left him at their shop at around 22:00 on Friday as he had been checking inventory.
“When he came back to the shop this morning he found their main entrance not locked, and saw that items were missing in the shop.”
The robbers took money, a cellphone, airtime vouchers and cigarettes.
A case of murder and business robbery was opened.
No arrests have been made yet.