In August 2011, a man in a baseball cap walked up to crowd watching an outdoor basketball game at the Kingsessing Recreation Center and began shooting. He fired 11 times, striking six people, before running away.
There were at least 500 witnesses to the assault. The city offered a reward of $20,000. Investigators went door-to-door attempting to gather information. And yet the shooter was never arrested.
"Everyone knew who did it," said St. Joseph's University sociologist Maria Kefalas, who, with two colleagues, spent three years studying the city's unwritten code of silence. "It was a combination of witness intimidation and an incredibly devastating blow to the relationship between the community and police. They're saying, 'We don't think you can keep us safe.'"
While the "Stop Snitching" T-shirts -- so prevalent here in 2005 -- have largely disappeared, the fashion of keeping quiet remains. Police and prosecutors cite silent witnesses, even those who are themselves the victims of crime, as a major problem in the city.
"Obviously, it makes it tough," Philadelphia Police Homicide Capt. James Clark said. "But there are always people who are going to come around and tell us and we have to keep digging until we find those people. ... Sooner or later, you'll get the right one to do the right thing."
Except sometimes you don't. Or when you do, that person pays the ultimate price.
That's what happened in January, when store clerk Reyna Aguirre-Alonso was executed in North Philadelphia. Aguirre-Alonso was known to have been questioned by police as a possible witness to an earlier homicide. One of the suspects arrested for her murder has also been charged in that death.
"It was a message," Kefalas said. "'This is what will happen if you talk to police.'"
But, she noted, when an Overbrook mother of four was shot and killed by a stray bullet in October, at least two witnesses did come forward. One told police, "I just feel bad about the lady getting killed." (The witnesses recanted during the suspect's preliminary hearing, but original witness statements can be used at trial.)
Kefalas said fear of retaliation isn't the only reason witnesses didn't come forward. In some neighborhoods, she said, residents feel the police are an "occupying force."
"'Stop snitching' is a byproduct of overpolicing," she said. "The police don't get cooperation because people see them as impotent and brutal."
One research subject compared calling police for help to pouring gasoline on a fire.
"We were disturbed and unsettled," Kefalas said, "that so many young people felt like, 'Gosh, you know, calling the police doesn't help someone like me.'"
For Kefalas' research, the team did interviews with 150 people ages 15 to 24, delinquent and non-delinquent. They found an unwritten set of rules governing when it's OK to give information to authorities and when it's not.
"It depends on context: two corner boys going at it and one shoots the other, no one going to cooperate," she said. "That's the rule of the game."