Darius D. Marshall, 19, of Dolton, Ill., surrendered Monday, the Chicago Sun-Times reported. He is charged with the first-degree murder of Eva Casara, 17.
The other suspects were already in custody.
Casara, girlfriend of Marshall's brother, Anthony Lee, 16, was shot during the bungled Christmas Day robbery, prosecutors say. She was 26 weeks pregnant and a girl, Leilani Paris Casara, was delivered before Eva Casara died Dec. 26.
Investigators said Marshall, Lee and a third brother, Diante Coakley, 21, went out to commit a robbery. Coakley and Casara got into the victim's car after she allegedly set up a meeting with him.
The victim, who was in the car with another passenger, ordered Coakley out and drove away, investigators said. The three brothers allegedly fired at the car while Casara was in the back seat.
The driver and his passenger realized Casara was still in the car when they heard a gurgling sound and dumped her on the street, prosecutors said.
Leilani Paris Casara was reported in critical condition.