Dr. Mengie Parker teaches criminal justice at North Carolina Central University. Before that he worked for the Durham Police Department as a gang expert.
He says graffiti Eyewitness News showed viewers Monday, which was sprayed on, under and near the Washington Street bridge, is likely written by young member of two gangs -- MS-13 and 18th Street.
Both gangs have roots in California.
"I would say these are probably 14 or 18, or around that range," Parker said. "And when you see this, this is a challenge. And if these two groups meet up somewhere at the same time, it's a good possibility that you may have some conflict."
Parker says such words between rival gangs can come to blows because "Whenever you put up graffiti, you have to be aware that there's another group who may come by and challenge you by crossing your graffiti out. And you have to be strong enough, or willing, to fight this group."
The paint on the bridge was removed Tuesday by the Police Impact Team.
Erasing all signs of the graffiti that used to be on the bridge is key, especially if done within 24 hours, according to Parker. He says that sends a very strong message from the city and police to the gang members.
Cleaning the graffiti shows the gangs that can't keep threatening each other with spray-painted messages.
Monday Durham Police told Eyewitness News they wouldn't comment on the graffiti while they are investigating it and they don't want to glorify gangs.
"Just to explain to citizens what's happening, I don't think that's glorifying a gang," Parker said. "You're not in anyway saying this is a good thing. You're not saying this is something people should aspire to."
He says with accurate, timely information, the community's motivated to report suspicious graffiti or activity.