Officer Michael Spicer told the judge that he had watched Thomas Pichardo take money from the driver of a car and hand over a small package, believed to be drugs.
Backup officers arrested the driver, who was carrying 28 packets of heroin, and grabbed Pichardo with $346 in cash, Spicer testified in Pichardo's September preliminary hearing.
Municipal Court Judge William Austin Meehan Jr. ruled that there was enough evidence to hold Pichardo, 33, for trial.
But on Friday, Pichardo, of the city's Juniata Park neighborhood, walked free.
His case was one of at least 11 that were dumped since District Attorney Seth Williams sent a private letter to Police Commissioner Charles H. Ramsey last week saying that Spicer and five other narcotics officers had lost their credibility and would not be called to testify in drug cases.
More cases are scheduled to be overturned this week, and the fallout could be breathtaking.
The officers - Spicer, Thomas Liciardello, Brian Reynolds, Perry Betts, Brian Speiser, and Lt. Robert Otto - were involved in at least 1,300 cases since 2006.
And that number may be just a fraction of their total cases.
Bradley S. Bridge, a veteran lawyer in the Philadelphia public defender's office, said the District Attorney's Office had indicated that it anticipated dismissing at least 17 cases involving the officers in which suspects are in custody.
"They are, appropriately, focusing immediately on getting people out of jail who should not be in jail," he said.
In his letter, Williams on Monday wrote that he was using "prosecutorial discretion" not to call the officers as witnesses.
"Also the Philadelphia District Attorney's Office will no longer accept any narcotics cases for charging when any of these police officers is a necessary witness," the letter said.
Williams did not specify why he had determined that the officers' credibility was too badly damaged for them to be called to testify.
Tasha Jamerson, Williams' spokeswoman, said last week that his office would have no comment on any aspect of the events involving the transfer of the officers.
The officers have not publicly commented, but John McNesby, president of the Fraternal Order of Police, Lodge 5, has said they have the full support of the union.
McNesby has reacted with fury to the decision, criticizing Williams for second-guessing the difficult and dangerous work done by members of the narcotics unit.
He also said the transfers stemmed from a dispute between the Police Department and the District Attorney's Office over the methods used by narcotics officers to target drug dealers. McNesby said that it was common practice for narcotics officers to use drug dealers to go after larger suppliers, and that the nature of their work makes narcotics officers vulnerable to accusations of corruption.
Several of the officers have been accused in federal lawsuits of planting evidence, fabricating police reports, and stealing cash from suspects.
Pichardo's case demonstrates the breakneck speed at which cases have been unraveling.
He was initially arrested in April 2006 but was on the lam for more than five years.
When he was finally pulled into court, Spicer was there to testify about how he collared Pichardo after the alleged drug deal at the Roosevelt Mall in Northeast Philadelphia.
But on Friday, attorney Lawrence Krasner persuaded Judge Michael Erdos in a special hearing to dump the case.
Krasner said he presented a copy of Williams' letter declaring that Spicer and the others were not acceptable witnesses, and Assistant District Attorney Lauren McHale agreed to drop the prosecution.
Krasner appeared in another court case last week and told the judge that Spicer and other officers with the police Narcotics Field Unit were involved in "things that were both illegal and outright crimes." He did not elaborate.
Municipal Court Judge Charles Hayden then freed two accused drug dealers.
In an interview Friday, Krasner said Pichardo had not previously been arrested and was not selling any drugs in the Roosevelt Mall incident.
He said Pichardo told him that Spicer and the other officers at the mall stole about $800 from him.
There were other accused dealers who walked last week.
One defense lawyer, who asked not to be identified, said the District Attorney's Office withdrew cases against four of his clients last week. In one case, he said, he had not even intended to ask for a dismissal, just a bail reduction. There was no explanation given other than Williams' letter, he said.
The lawyer said he intended to file motions to move up the court dates on some of his open cases involving the officers, to get those clients out of jail sooner.
"It seems like what's happening is a carte blanche erasing of these cases," he said. "It's very sudden."
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Inquirer staff writer Dylan Purcell contributed to