Martin Cobb and his sister were playing together in their backyard, on the railroad tracks that ran behind their house, when the suspect approached them and accosted the girl, police said.
According to authorities, when the boy tried to help his sister, the suspect struck him in the head with the brick.
The boy died at the scene.
The girl was taken to the hospital.
Tracy Lightsey, a neighbor, said the brother and sister were inseparable.
“He felt like he was his sister’s protector. He was his sister’s keeper till his death,” she told the Richmond Times-Dispatch.
Police searched for the suspect Thursday night, who was initially described as a white male with scraggly facial hair, though investigators say the victim was threatened by her attacker into providing false information, and the description had been amended to a black male teenager.
A warrant was obtained for a suspect believed to be connected with the crime, who is now in custody and undergoing medical evaluations according to a local CBS affiliate.
Anyone with additional information is asked to call Crime Stoppers at 804-780-1000 or text Crime Stoppers at 274637, using the key word “ITip” followed by the tip.