Edwards, 16, admitted his guilt in the Feb. 13 crime spree and will be sentenced to 51 years in prison.
His co-defendant, 19-year-old Sirquain Burr, also pleaded guilty and will receive 59 years in prison.
Prosecutors said they believe Burr fired the fatal shot.
"We believe based on his involvement in the other robberies, he was most likely the triggerman in the homicide. We don't know 100 percent for sure. It was Gabriel Edwards’ DNA that was found on the gun after it was tossed. But we think it was most likely because he tossed the gun," deputy prosecutor Jeremy Teipen said.
"This should send a message to everyone. Be careful who you hang out with. It's not important that you are the triggerperson. You could be the person with the triggerperson and by hanging out with them, being with them you could be held equally responsible and that's exactly what happened today," Kenneth Riggins said.
Burr will be formally sentenced July 11 and Edwards will be sentenced July 16.