Joseph Carmoney is charged with aggravated robbery in that incident.
He's also charged with robbery for an incident that occurred about one week after he allegedly broke into his grandparents' house.
Officers say a woman who lives in the 36-hundred block of Glenwood St. told authorities three masked men entered her home.
She said one man shined a flashlight in her eyes so she couldn't see, while the other two rummaged through her home.
Several days later and during the police investigation, the elderly couple told officers they thought their grandson, Joseph Carmoney, could have committed the crime.
When Carmoney was arrested for the second robbery, police say they asked him about the robbery of his grandparents' home.
They say he first denied knowing anything about it, but then admitted he and two accomplices sneaked in through a back window and used a firearm with a flashlight attached to it to distract his grandmother.
He's jailed on $775-thousand in bonds.