The stories documented conviction rates that are among the lowest in the nation and described how thousands of cases collapse after reluctant or terrified witnesses fail to appear in court. When witnesses do appear, they often recant their earlier statements to police.
In one homicide case highlighted by the newspaper, a witness disavowed his testimony after seeing his statement to detectives posted with a threatening message in a restaurant in his neighborhood.
Another witness in the same case was murdered 10 days after testifying at a court hearing. The victim was among 13 witnesses or their relatives killed in Philadelphia in the last decade.
City prosecutors filed witness-intimidation charges against about 1,000 people between 2006 and 2008 but won conviction in only about a quarter of all cases.
Specter's bill would allow federal prosecutors and the FBI to investigate and bring charges against people who intimidate witnesses in local court cases and would set tough new penalties for those crimes.
It would impose maximum penalties of up to 20 years for intimidating or harming a witness, up to 30 years for the attempted murder of a witness, and the possibility of the death penalty for the murder of a witness.
Specter called the situation in Philadelphia "disastrous" but said the problem was pervasive nationwide.
Philadelphia District Attorney Seth Williams lauded Specter's efforts.
"As a former Philadelphia D.A., I think he, more than most, understands what we are dealing with on a daily basis," Williams said. "So I appreciate his effort."
Barbara Clowden, whose 17-year-old son was killed two days before he was to testify as a witness in an arson trial in 2006, said she welcomed Senate efforts to strengthen penalties for witness intimidators.
"I support it 100 percent," she said. "The federal government handles things totally differently than the local courts do. Had the federal government been involved in the very beginning, my son might not be dead, and if the FBI had been involved, I believe there would have been an arrest."
Clowden, profiled in the Inquirer series, told her family's story publicly at a Senate subcommittee hearing Specter convened to explore ways to combat witness fear.
Joining Specter as cosponsors were three other Democrats, Charles E. Schumer of New York, Ted Kaufman of Delaware, and Amy Klobuchar of Minnesota, once the top prosecutor in Minneapolis.
Specter is running for a sixth term as a U.S. senator. He is facing opposition in the Democratic primary this spring from U.S. Rep. Joe Sestak of Delaware County, who also held hearings on issues raised in the series.
Under federal court precedent, the Specter measure could be invoked only in cases in which the crime has some link to interstate commerce.
Specter drafted the bill broadly to maximize its potential use. It would apply when a threat is leveled by phone or e-mail, when a perpetrator crosses state lines and almost always when a gun is used. The bill says it would apply if a gun at any point had been shipped across state lines.
"When a gun is involved, it is conclusively federal," Specter said in an interview.
Specter is also supporting legislation to provide $30 million in federal money yearly to help local prosecutors protect and relocate witnesses.
The measure passed the House last year by a vote of 411-12 but has stalled in the Senate. It is to be taken up Thursday by the Senate Judiciary Committee, of which Specter is a member. Specter aides say they expect it will pass this year.
In Philadelphia, funding to relocate witnesses has been cut almost 25 percent in the past two years.
Contact staff writer Nancy Phillips at 215-854-2254 or firstname.lastname@example.org.