Demetrius Warren, 17, has not been charged with the killing of Amadou Cisse, the Chicago Tribune reported. A co-defendant, Eric Walker, 16, was charged as an adult with murder Wednesday.

Prosecutors allege the two teens committed a series of robberies around the university. They allegedly cruised the neighborhood in a Pontiac Bonneville with three others who have not been charged.

Cisse, a native of Senegal who was close to earning a doctorate in chemistry, was gunned down near the campus Nov. 19. On Friday, the university held a memorial service.

Czermy Brasuell, an administrator at Bates College in Maine, where Cisse earned his bachelor of arts degree, said he would have been concerned about his killer.

"Amadou would be grieving for that child who has been charged with his death," Brasuell said. "Amadou would ask, 'How does it come to pass that no one taught this young man another path?' He would ask of us, 'How can we save this child?'"