“It had seemed like the city was trending in the right direction, but when you see this, anybody who lives in the city of Chicago is going to be concerned,” said Jens Ludwig, the Crime Lab’s director.

At a news conference on Monday, the police superintendent, Eddie Johnson, and the mayor, Rahm Emanuel, sought to place much of the blame for the weekend carnage — and for the still-high rate of violent crime — on factors other than the police department or the city government, citing too many guns in circulation, the failure of courts and judges to convict and hold accountable those caught with illegal guns, and the need for better parenting.

“We need everyone, especially our judicial partners, to start making repeat gun offenders feel consequences for their actions,” Mr. Johnson said, adding: “We need everyone to come to the table with less talk, but more action.”



They said, too, that people in the neighborhoods with the most violence needed to “step up” and help the police solve these crimes. But community leaders, civil rights groups and critics of the police say those statements belie a deeper problem: That the police have given the people who live in the neighborhoods hardest hit by the violence little reason to trust them. Chicago has one of the lowest rates of solving murders of any major city in the country.

In many places, constructive interaction between the community and the police rarely happens, they say, adding that officers react in force to shootings but virtually disappear when it comes to crime prevention, community policing and, often, investigations.

The police have maintained for years that an endemic “no-snitch” culture keeps them from solving more serious violent crimes. Many residents are afraid to help because they believe there is little the police would — or could — do to protect them from retaliation.