Dowery had been shot in the back and in both arms and legs—six times in all. Only the skilled hands of the surgeons at Johns Hopkins spared his life. And yet, in the eyes of many people in the blocks around Bartlett, John Dowery had gotten what was coming to him.

In many Baltimore neighborhoods, talking to the law has become a mortal sin, a dishonorable act punishable by social banishment—or worse. Prosecutors in the city can rattle off a litany of brutal retaliations: houses firebombed, witnesses and their relatives shot, contract hits on 10-year-olds. Witness intimidation, they say, badly hampers their ability to fight crime, and it affects nearly every murder case they try.

Prosecutors in most major U.S. cities tell similar stories. Two years ago in Philadelphia, a drug kingpin was convicted of witness intimidation after he was taped threatening to kill those who testified against him. Five relatives of one witness in the case had already died, in a house fire that prosecutors believe was the drug lord’s doing. Last year in San Francisco, two gang members beat a murder rap after the state’s star witness turned up dead. Several years ago in Denver, a key homicide witness was sexually assaulted in what prosecutors believe was a “contract” attack designed to frighten him out of testifying.

Police and prosecutors have been contending with reluctant witnesses for decades. But according to law-enforcement experts, the problem is getting dramatically worse, and is reflected in falling arrest and conviction rates for violent crimes. In cities with populations between half a million (for example, Tucson) and a million (Detroit), the proportion of violent crimes cleared by an arrest dropped from about 45 percent in the late 1990s to less than 35 percent in 2005, according to the FBI. Conviction rates have similarly dropped. At the same time, crime has spiked. Murder rates have risen more or less steadily since 2000. Last December, the FBI voiced concern over a jump in violent crime, which in 2005 showed its biggest increase in more than a decade.

The reasons for witnesses’ reluctance appear to be changing and becoming more complex, with the police confronting a new cultural phenomenon: the spread of the gangland code of silence, or omerta, from organized crime to the population at large. Those who cooperate with the police are labeled “snitches” or “rats”—terms once applied only to jailhouse informants or criminals who turned state’s evidence, but now used for “civilian” witnesses as well. This is particularly true in the inner cities, where gangsta culture has been romanticized through rap music and other forms of entertainment, and where the motto “Stop snitching,” expounded in hip-hop lyrics and emblazoned on caps and T-shirts, has become a creed.

The metastasis of this culture of silence in minority communities has been facilitated by a gradual breakdown of trust in the police and the government. The erosion began during the civil-rights era, when informants were a favorite law-enforcement tool against groups like the Black Panthers. But it accelerated because of the war on drugs. David Kennedy, the director of the Center for Crime Prevention and Control at the John Jay College of Criminal Justice, in New York, told me: “This is the reward we have reaped for 20 years of profligate drug enforcement in these communities.” When half the young black men in a neighborhood are locked up, on bail, or on parole, the police become the enemy. Add to this the spread of racialized myths—that crack was created by the CIA to keep blacks in their place, for example—and you get a toxic mix. Kennedy thinks the silence of many witnesses doesn’t come from fear, but from anger.