Georgia homicide detectives are trying to determine why a 13-year-old honor student was shot to death in front of his home by a man with a shotgun.

The killer was wearing a ski mask when he walked up to Brayan Zavala Thursday evening in Riverdale and shot him in the face, Clayton County police said. The boy died in his father’s arms.

On Sunday, police assigned to the case issued an appeal to the public for tips. The shooting occurred days before Brayan's 14th birthday.

LOUISIANA MAN CHARGED WITH SHOOTING AND KILLING TODDLER DURING VIOLENT RAMPAGE

"They shot my brother, they killed him. For no reason," Brayan’s 16-year-old brother told Fox 5 Atlanta.

"He shot my brother in the face,” Jesus Zavala said. “My brother dropped and I saw his eyes also drop. We lost him."

PENNSYLVANIA WOMAN, 19, KILLED IN ATTEMPTED CARJACKING

The shooting took place in front of the Zavala mobile home. Jesus said he and Brayan were helping their father fix a riding mower.

Jesus said the shooter never responded when his father asked him what he wanted, the station reported.

CLICK HERE TO GET THE FOX NEWS APP 

The shooter made his getaway in an SUV without license plates, which apparently had been removed.