Edward Ryals Jr. was given an 18-year prison sentence after he pleaded guilty to second-degree murder on Thursday.
Ryals was 18 when police said he killed Ronald Blackmon Jr. in early March 2011.
He entered the plea before Criminal Court Judge Rebecca Stern.
The victim was shot in the head in what police said was a gang-related incident.
The victim was taken to a hospital, where he later died.