Across the country, gangs have grown to about 1 million members, according to the federal government's most recent count in 2009, and law enforcement officials say that number is increasing.
The 25% jump in the membership ranks from 2005, recorded by the National Gang Threat Assessment, defies the steep decline in violent crime. That has sunk to its lowest levels since 1973, according to a National Criminal Victimization Survey released last month by the Justice Department.
Violent crime declined to 17.1 incidents per 1,000 people in 2009, down from 19.3 incidents in 2008, the report says.
"With gangs usually comes a lot of violence; we're looking at this very closely," says John Moore, director of the National Gang Center, an arm of the Justice Department. He says national surveys of gang membership continue to show growth.
Just as a spike in crime did not follow the nationwide financial crisis, Moore says, violent crime has not followed expected patterns linked to the proliferation of gangs.
In Chicago, where gang membership is up to 105,000 this year from about 70,000 in 2000, murders are on pace to drop to the lowest levels since 1965, Police Superintendent Jody Weis says. The 343 murders this year are eight fewer than this time last year, Weis says.
Among the reasons, Police Commander Leo Schmitz says, is that some gang leaders — including those ordering murders and other retaliatory attacks — are serving long prison sentences.
Their absences, Schmitz says, have contributed to disorganization in the ranks and cause some lower-level operatives to form their own groups with new members, a factor driving an increase in Chicago gang membership.
"We've taken out so many of the leaders — stone cold killers — that it has fractured some of these organizations," Schmitz says.
In Los Angeles, Police Detective Jorge Luis Martinez says gang membership in the city is up to about 45,000 this year from about 43,000 in 2008, while murder and other violent crime decline. This year, the 231 murders represent an 8% decline from the same time in 2009 and 24% fewer than in 2008.
Martinez says the city's "fragile peace" is being aided by a combination of strategies designed to reduce the violence.
One of the programs involves the use of former gang members, who respond to shooting scenes to help calm victims' friends and relatives in an attempt to prevent retaliatory attacks.
Martinez says the former gang members do not work for police and are not there as informants for police. Yet he says their work has helped break a cycle of warfare.
Police in Los Angeles and elsewhere also have expanded their use of restraining orders, restricting the activities of gangs in certain areas of the city.
"We've been very fortunate so far," Martinez says. "We're going in the right direction." | 
