LITTLE ROCK - The FBI has joined an investigation into the road-rage killing of a 3-year-old boy, who police say was fatally shot while riding in the backseat of his grandmother's car in Little Rock, Arkansas.

The FBI also announced Monday that it's offering a $20,000 reward in the case. The city of Little Rock is also offering a $20,000 reward.

Authorities say the boy and his grandmother were on a shopping trip Saturday when a driver opened fire on the grandmother's car after honking at her at a stop sign. The child was pronounced dead at a hospital.

Police say the shooting appears to be random and that the suspect was driving an old black Chevrolet Impala.

No arrests have been made.