Up to 80 percent of Chicago murders and non-fatal shootings are gang- related, primarily young black and Hispanic men killed by other black and Hispanic men.

FORBES: Disarming Realities: As Gun Sales Soar, Gun Crimes Plummet

Sao Paulo, Brazil (CNN) -- For many it's the adrenaline, the thrill of scaling buildings to scrawl their gang's signature in huge black letters from the highest point possible.

CNN: Wall art masquerades as class war

Jeff Carr, who heads the mayor's Gang Reduction and Youth Development program, says 90 percent of LA's gang-related crime is "primarily black on black and brown on brown, " and not across racial lines.

CNN: Dad faces son's alleged killer; sees 'normal' youngster

The city's homicides were 80% gang-related, and 80% of the victims were black, although only 33% of the city's population is black.

BBC: New York murders at record low