The boy, Brayan Zavala, was working in his front yard on a lawnmower along with his 16-year-old brother.
Brayan — who was pronounced dead at the scene — would have turned 14 in the next few weeks.
What are the details?
Riverdale authorities are furiously working to identify the suspect who killed Brayan.
Brayan's brother, Jesus, told WXIA-TV that a masked suspect pulled up to the family's home, pulled out a gun, and shot the boy in the face.
He told WSB-TV, "What did ... what did he do? We were working on a lawnmower, and all of a sudden, my brother is dead."
"The shooter didn't even say 'I want your money' or 'This is a robbery' or 'I'm assaulting you,'" the teen recalled according to WXIA. "He just came there, stood in silence, and shot my brother."