Witnesses say Robinson died shielding two younger children from bullets fired at the car they were riding in. The driver of that car has talked about what happened.
Robinson had gone to watch his 18-year-old cousin play in a Simeon high school basketball game. He was on his way back to his aunt's house when he was killed.
Driving the car was Robinson's cousin, Brittany Orange. She says, if it wasn't for Robinson's heroic action in the back seat, her 10-month-old son and 4-year-old goddaughter may not be alive today.
"I know you're not coming back, but Greg, you save my baby's life," Orange said tearfully Sunday.
Orange says her cousin Greg Robinson is a hero. She also says she was less than a block away from home when someone opened fire with what police believe was assault rifle.
"It was rapid. Boom, boom, boom, and just never stopped," said the victim's aunt, Rhonda Orange-Coenic, who could hear the shots from her house.
Sunday night, the family, along with a community activist, announced they were offering a $2,000 reward for information leading to an arrest and conviction.
"If this $2,000 means that much to you for you to step and say, 'My son did this' or 'My nephew did this,' then take the $2,000," Orange-Coenic said.
Orange-Coenic is also calling for gun control and parental responsibility to stop another teenager from being killed.
"If you take account of what your child is doing, then maybe we wouldn't have this many," the aunt said.
The call for parents to step up and stronger gun calls was echoed by Yolanda Sepulveda, who lost her 15-year-old grandson last year.
"So many innocent children who had a life, a future, who had good hearts were robbed of that. Is that fair? What is the city coming to?" she said.
Greg Robinson was a freshman at Simeon high school. He is the 28th Chicago public school student killed this year.
"Please turn yourself in. My cousin didn't deserve this," said Brittany Orange.
Brittany Orange says there were so many bullets fired at her car, she kept driving until the guns stopped.
Police do not believe Robinson or anyone in the car was the intended target.
The anti-violence group CeaseFire says, based on their information, they do not believe the shooting was gang-related.
Chicago police were not commenting Sunday on a possible motive.