The shooting of Haji Mohamud happened early Saturday after a party outside a Las Vegas apartment complex, the Las Vegas Sun reported.
Metro Police Lt. Ray Steiber Wednesday pleaded for witnesses to come forward.
"There are people out there -- who were there -- that know exactly what happened ... and who killed a 14-year-old boy," Steiber said. "There's parents out there who may have overheard their children talking about what occurred that night. ... We're asking for anybody with information to come forward and help your community."
Steiber said police know Mohamud was attending a birthday party, during which some of the approximately 100 guests became rowdy and the host asked everyone to leave.
As Mohamud and other guests stepped outside, 20 bullets were fired. Mohamud was hit in the head and died. An 18-year-old man was injured in the incident.
Steiber said as many as three gunmen were involved in the shooting.
"I think there is information being withheld," Steiber said. "It's hard for me to believe that over 40 people were there -- and at one point over 100 -- but nobody saw anything."