"I'm pleading with the community because we do know that someone in the community knows who did this. So please, please step forward. You can do it in a way where you don't have to give your name, but please step forward so that we can at least bring closure," said the Rev. Michael Fisher with the Greater Zion Family Church.
Authorities believe the suspects may be gang members, though they do not think Duncan was in a gang. He just happened to be walking down the street when the suspects were driving by.
"They made comments to the victim. The victim walked towards the vehicle to see who it was. Then suddenly, one person from the vehicle fired a shot, hitting Oscar in the head," said Lt. John Radtke with the Los Angeles Police Department.
Los Angeles Councilmember Bill Rosendahl is asking fellow council members for $50,000 in reward money for information that leads to an arrest.
Meanwhile, those who knew Duncan best want everybody to know the kind of person he was. Duncan worked for the Boys & Girls Club in Venice, as well as the Takeover Youth Ministry in Inglewood.
The young man dedicated to helping kids find a better life lost his own, and family members and authorities are convinced somebody out there knows why.
Police do not have much evidence to work with, but they say the suspects are likely African American and were driving in a white sedan.
If you have any information about this case, you're urged to contact detectives with the West Homicide Bureau at (213) 382-9470.