Prosecutors dropped murder charges today against an ex-FBI agent accused of feeding confidential information to a homicidal mob informant in what was billed as one of the worst law enforcement corruption cases in American history.

Lindley DeVecchio, who had denied the charges for years, heard the news in a Brooklyn courtroom one day after a key government witness, mob moll Linda Schiro, had her testimony undermined by a taped interview she gave to reporters a decade ago.

As Mr. DeVecchio stood in the courthouse well after the judge granted prosecutors’ request to drop the charges, there was applause — much of it from former FBI agents who worked side by side with him.

“We all knew he was innocent,” a former colleague, Jim Kossler, said. “This never should have happened. Never.”

Ms. Schiro testified earlier this week that Mr. DeVecchio had fed her gangster boyfriend, Gregory Scarpa, secret FBI intelligence that was then used to kill four suspected rats or rivals in the Colombo crime family. But this week, journalist Tom Robbins revealed in the Village Voice that Ms. Shiro had provided him with a different account during a 1997 interview.

“Had we been provided these tapes much earlier in the process, I dare say we wouldn’t have been here,” Assistant District Attorney Michael Vecchione said.

It was a stunning collapse of the case against Mr. DeVecchio in the midst of his trial.

Prosecutors had claimed Mr. DeVecchio was plied with cash, jewelry, and hookers by Scarpa in return for the confidential FBI intelligence that was then used in the killings during the late 1980s and early ’90s.

The 1997 interview with Ms. Schiro became the focus of a legal fight yesterday when defense attorneys announced they had subpoenaed tapes of the question-and-answer session, hoping the tapes would undermine her crucial testimony against Mr. DeVecchio.

The interviews were conducted by reporters Tom Robbins and Jerry Capeci. Mr. Robbins revealed their existence in a Village Voice piece published this week.

“One thing is clear: What Linda Schiro is saying on the witness stand now is not how she told the story 10 years ago concerning three of the four murder counts now at issue,” Mr. Robbins wrote in a story headlined “Tall Tales of a Mafia Mistress.”

Prosecutors and defense attorneys listened to the tapes behind closed doors in an effort to determine how damaging they would prove to the prosecution’s case. Ms. Schiro had been expected to undergo a second round of cross-examination, but court was canceled for the day.

Defense attorney Douglas Grover predicted the tapes would fully discredit Ms. Schiro and vindicate Mr. DeVecchio, who has consistently declared his innocence.

“We’re just thankful that it’s all come out,” he said.

In her testimony, Ms. Schiro, 62, said she would regularly sit in on weekly meetings between Mr. DeVecchio and Scarpa, who died in prison in 1994. She also said she overheard the agent warn her boyfriend about potential rats and rivals in a power struggle within the Colombo family, including the four slaying victims.

But the Village Voice reported that in the 1997 interview, Ms. Schiro linked Mr. DeVecchio to only one of the slayings in the indictment. For instance, when asked about one victim, she insisted the agent had nothing to do with it. “Lin did not tell,” she said.

Because a person can’t be tried twice for the same crime, Mr. DeVecchio is free and clear of the charges. Ms. Schiro could face possible perjury charges, Mr. Vecchione.

State Supreme Court Justice Gustin Reichbach said he had no choice but to approve prosecutors’ request to drop the charges, but expressed disgust with the long relationship between the FBI and its informant.

“That a thug like Scarpa would be employed by the federal government to beat witnesses and threaten them at gunpoint to obtain information … is a shocking demonstration of the government’s unacceptable willingness to employ criminality to fight crime,” the judge said.