Philadelphia prosecutors are wielding a new tool to combat the city's "no snitch" culture - using grand juries to shield witnesses from threats by allowing them to testify in secret.

In scores of cases in 2013, the District Attorney's Office has been deploying a 23-member grand jury to file charges in selected violent crimes - when prosecutors claim witnesses have been intimidated or are likely to face threats.

The use of the indicting grand jury means witnesses in these cases are now testifying in secret and face no cross-examination. Neither suspects nor defense lawyers are allowed in the room.

Charges are leveled by a simple majority vote of the jury. For the targeted defendants, this supersedes the standard practice, in which judges uphold or dismiss charges after preliminary hearings. Those hearings include public testimony by victims and witnesses.

District Attorney Seth Williams was the first county prosecutor in Pennsylvania to impanel such a grand jury after the state Supreme Court joined 48 other states and authorized them last year. Prosecutors in Montgomery County, Chester County, and the Pittsburgh area are exploring the idea.

"The indicting grand jury is a very useful, very powerful, tool for law enforcement and we are going to be using it," Michael Noone, first assistant district attorney in Chester County, said Friday.

The two Philadelphians on the state Supreme Court - Chief Justice Ronald D. Castille and Justice Seamus P. McCaffery - pushed for the overhaul in response to a 2009 Inquirer investigative series that portrayed criminal courts as plagued by rampant witness fear, a massive number of fugitives, and the early collapse of thousands of cases yearly.

It found that in Philadelphia, defendants charged with murder, rape, robbery, and serious assaults were walking free on all charges in nearly two-thirds of all cases. Among the nation's most populous counties, the city had the lowest felony conviction rate.

In Philadelphia, prosecutors have used the grand jury to indict about 100 defendants, including an alleged mob soldier charged with murder and a day-care operator accused in the drowning of a child.

John Delaney, a top prosecutor with the city District Attorney's Office who helped launch the approach, said it was designed to curtail the witness intimidation that ruins so many criminal cases.

"It's a rebalancing of the citizens' and the defendants' rights," Delaney said.

The city's defense bar says the recalibration is way off. Top lawyers say the new system has the potential for abuse and chips away at basic rights, especially the right to confront one's accuser.

"It makes the job easier for the police and prosecutors," said Jeffrey M. Lindy, a veteran defense attorney. "Sometimes, easier is good. But sometimes, when it comes to constitutional mandates, easier is not better."

The jury indictments are perhaps the most dramatic in a host of new procedures approved by the state Supreme Court in recent years. That overhaul has shaken up a criminal court system that, according to its critics, failed at its core function of trying cases on their merits.

Indicting grand juries were abolished in Pennsylvania in 1976 in what was touted as a reform, with the aim of streamlining the court system. The reauthorization of them last year by the state Supreme Court leaves Connecticut the only state to bar indicting grand juries. Federal prosecutors also use such juries to bring charges.

In giving the prosecutors in the state's 67 counties authority to indict via grand juries, the Supreme Court limited their use to cases where witness intimidation was a factor.

To meet that rule, prosecutors have been filing sealed motions with Common Pleas Court Judge Jeffrey P. Minehart, who presides over the grand jury. The motions, required for each case, attest that witness intimidation has happened, is happening, or is likely to happen.

Prosecutors say they are using their new authority sparingly. The office is on track to indict 500 defendants a year - a small share of the 18,000 people arrested for violent crimes annually in Philadelphia.

Defense lawyers say the rules are tilted too far toward the prosecution. They worry that a stream of cases could become a flood.

"One can make an argument that witness intimidation is going on in any case," said Philadelphia lawyer Michael J. Engle, a former president of the state Association of Criminal Defense Lawyers. "No one has a crystal ball. So it creates a speculative standard."

Because the motion from prosecutors is secret, the defense has few effective ways to challenge the prosecution's facts or forecast, Engle said.

But Kirsten Heine, chief of the district attorney's charging unit, said making the allegation public might put witnesses at risk and defeat the purpose of the initiative.

Heine is supervising the grand jury with fellow prosecutor Jacqueline Coelho.

In an interview last week, Heine, Delaney, and Deputy District Attorney Laurie Malone, head of the pretrial division, noted that witnesses will still have to appear in open court for the defendants' trials.

Despite extensive efforts to encourage more witnesses to come to court in recent years, prosecutors say fear remains a debilitating virus.

Witnesses who "snitch" face abuse, retaliation, and, not uncommonly, death.

In recent days, a Common Pleas Court judge, Charles Ehrlich, revoked bail for an accused gun trafficker after prosecutors said they twice heard him call a witness a "snitch" in court.

And during a recent murder case, prosecutors said, someone surreptitiously photographed a witness on the stand and uploaded it to an Instagram account. The next day, witnesses were digitally filmed via a cellphone camera in the courtroom hallway.

In another move to cut down on intimidation, Heine said, prosecutors are asking judges in the indictment cases to ban defense lawyers from giving their clients copies of witness statements. The attorneys may only read the statements to the defendants.

At times, such statements have ended up being posted in neighborhoods or stuck on walls inside prison cells.

The prosecutors have also pushed back by several months the date they turn over evidence - a tactic defense lawyers say has hurt their ability to investigate and plan their court strategy.