William D. Strickland, who admitted stealing his grandfather's gun for the attack, has been charged with first-degree murder and armed robbery.
Strickland's grandfather, also named William Strickland, was shot at 3:30 a.m. March 2 outside his home. The 72-year-old victim was waiting for a bus to take him to his weekly dialysis appointment when he was attacked, the Tribune reported.
The grandson then took his grandfather's belongings and used the money to buy tattoos and shoes.
The suspect was a member of a local gang, but had no criminal history, the Chicago Sun-Times reported.
He was living with his grandfather at the time of the slaying.