(CBS News) CHICAGO - Jesse Jackson is calling on President Obama to come to Chicago to confront the city's gun crisis. On Saturday, Jackson led marchers to the park where a 15-year-old girl was shot to death this week, a mile from the president's Chicago home. The police say she was likely the a victim of a gang turf war. We learn why gang-related murders have become so difficult to solve.
For almost seven years, Pam and Tom Bosley have been hoping for a measure of justice.
"My son Terrell was murdered April 4, 2006," said Pam.
But no one has paid a price except Terrell's family.
"The first year when this happened to Terrell, it was real hard for me. And I tried to take my life twice," said Pam.
A suspect was arrested and tried but then acquitted. The evidence was sparse -- the witnesses willing to testify few -- even though Terrell was shot in a church parking loot on a busy street.
"People were out there," said Pam. "But nobody said anything. People were coming home from work, they was driving by. So you had to see somebody running down the street with a gun and shooting it."
In many of these murders, a code of silence descends like a burial shroud.
"People don't want to cooperate," said Tom Byrne, Chicago's chief of detectives. "Gang bangers have a no snitch code. People that live in the community -- the good people- - they may be fearful."
About 87 percent of Chicago murders involve shootings and they can be especially hard to solve.
"All we may have would be a casing and unfortunately a blood swab from the victim, and that's it," Byrne said.
Twenty years ago, Chicago's homicide rate was much higher, but the arrest rate was as well - 60 percent in 1992. Last year, it was just over 25 percent.
Police Union Vice President Daniel Gorman blames years of budget cutbacks. "Statistics show that we don't have enough cops," he said.
Next week, the city will add 70 new detectives to the force, the first addition since 2007. But Gorman said Chicago needs at least 200. Without them, "the murder rate's gonna keep going, and the clearance rate is going to continue to fall," he said.
And that's almost an incentive to the shooters who know as well as the cops that three out of four times, they'll get away with it.