Federal prosecutors on Tuesday shed another problematic witness against six Philadelphia narcotics officers accused in gang-style beatings and robberies of drug suspects, prompting renewed calls from defense lawyers that the entire case should be tossed.

Citing "contradictions" in his story, prosecutors withdrew all charges stemming from the grand jury testimony of Christian Cirigliano, a South Philadelphia man who said the accused officers kicked in his door and stole $3,200 from him on March 7, 2010. His story kept changing, depending on the audience.

The government's decision to excise Cirigliano - made as jury selection began Tuesday - was the second black eye suffered in less than a month by one of the highest-profile federal police corruption probes in Philadelphia in recent years.

It also underscored what defense lawyers have cited as the chief weakness of the government's case: the criminal backgrounds and unreliability of many of the accusers.

And, argued defense lawyer Michael Diamondstein at a last-minute hearing Tuesday before U.S. District Judge Eduardo Robreno, prosecutors should have seen this one coming.

"Quite frankly, the evidence of perjury was staring the government right in the face," he said. "They chose to ignore it."

Publicly available court records show that Cirigliano, 36, told three different stories to different courts about the 2010 encounter.

Details of his testimony varied significantly from his own 2012 trial on drug charges stemming from that incident, to a civil suit he brought against the indicted officers the following year, and again in his retelling of the events before the grand jury that handed down the federal indictment last year.

For instance, at trial and in his lawsuit Cirigliano did not mention the money the officers allegedly stole from his house, which would later become the centerpiece of his grand jury testimony in the federal case.

He also told grand jurors that he had prescriptions for the Percocet pills seized from his home, and that the indicted officers removed labels from the bottles to make it appear that he had obtained them illegally. In his criminal trial, Cirigliano testified that he bought the pills illegally from customers outside of a pharmacy.

In court filings, Diamondstein called the government's decision to withdraw charges tied to Cirigliano weeks before trial "nothing less than an attempt to hide and whitewash a fraud that was - be it negligently or recklessly - played upon the grand jury."

But Assistant U.S. Attorney Anthony Wzorek bristled at the suggestion that he knowingly allowed a witness to perjure himself to bolster the indictment. He maintained he only became aware of Cirigliano's civil suit this month.

"We look forward to answering that" allegation, he said. "We look forward to making ourselves available - on the witness stand if necessary - to answer that."

Still, said Jeffrey Miller, a lawyer for Thomas Liciardello, an indicted officer, the problems with Cirigliano are not the first that prosecutors have encountered with their witnesses and should raise questions about the testimony of other government witnesses.

Earlier this month, prosecutors dropped another of the officers' accusers - Warren Layre, owner of a West Mount Airy machine shop - after he was charged in a Montgomery County drug investigation.

"Counsel should be permitted to show the jury that [Cirigliano] sold the FBI a bill of goods and ask whether any of the other underworld figures upon which this prosecution is built have done the same," Diamondstein wrote in a motion making a similar argument.

Robreno on Tuesday allowed the government to withdraw the Cirigliano counts, but withheld judgment on whether that decision should have any bearing on the larger indictment.

Prosecutors believe they still have a strong case against the six indicted officers.

In a sweeping indictment involving 20 other purported victims, they allege that between 2006 and 2012, the group stole more than $500,000 in cash, drugs, and property from drug suspects, and falsified reports to cover their crimes.

Those who resisted their demands, the government says, were dangled over balconies, threatened with seizure of their homes, held in dank hotel rooms for days, or beaten while officers kept score on who could inflict the most debilitating injuries.

Since the federal case against the officers surfaced last year, local courts have tossed about 450 of their arrests, and dozens of people have filed federal civil rights lawsuits against them.

While there is no denying many targeted by the crew have lengthy criminal pasts, prosecutors say they can win convictions at trial based on the sheer volume of allegations.

What's more, a onetime member of the narcotics unit - Jeffrey Walker - has pleaded guilty to attempted robbery and gun violations and is expected to testify against his former colleagues.

Still, the removal of Cirigliano from the case appeared likely to brighten the prospects of at least one of the indicted officers. Cirigliano was the only government witness to link Officer John Speiser to any of the alleged crimes.

Diamondstein, Speiser's lawyer, urged Robreno to toss the remaining case against his client.

"The evidence against Mr. Speiser is virtually nonexistent," he said. "Now the witness who offered the most incriminating evidence against Mr. Speiser has been exposed as an immoral, despicable, and opportunistic liar."

Wzorek, however, said that while no other witnesses testified to having seen Speiser during alleged attacks by the crew, the officer put himself at two other scenes tied to incidents now charged in the indictment by drafting the police reports for the arrests. Prosecutors have singled both reports out as fraudulent accounts drafted to cover the officers' alleged crimes.

Aside from Speiser and Liciardello, the defendants include Officers Brian Reynolds, Michael Spicer, Perry Betts, and Linwood Norman. All have denied the charges.

Jury selection in the case continues Wednesday. Testimony, in what is predicted to be a 10-week trial, is to begin March 30.

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