The technology banker most associated with the dot-com boom, Frank Quattrone, faces the prospect of a third trial after a federal appellate court overturned his conviction on obstruction of justice charges yesterday.

The 2nd U.S. Circuit Court of Appeals ruled that a judge gave incorrect jury instructions during Mr. Quattrone’s May 2004 trial. The charges came about after Mr. Quattrone sent an e-mail in 2000 urging fellow bankers to destroy records that the government sought in an investigation. Mr. Quattrone is not believed to have seen the document request.

When the jury convicted Mr. Quattrone two years ago on charges connected to the e-mail, the Credit Suisse First Boston banker had already stood trial once. The earlier trial in 2003 had resulted in a hung jury.

The office of U.S. Attorney Michael Garcia in Manhattan did not indicate whether it would seek a third trial or drop the case. A spokeswoman for the office, Heather Tasker, said, “We’re reviewing our options.”

A professor of law at Columbia University, John Coffee, said he anticipated that prosecutors would likely seek a third trial because the appellate court did not fault the evidence that the prosecution submitted.

Mr. Quattrone, 50, made his fame and fortune during the dot-com boom of the 1990s, when he was the lead banker on initial public offerings for companies such as Amazon and Cisco. In 2000, as federal investigators began examining CSFB’s relationship with certain investors, Mr. Quattrone had oversight of more than 400 investment bankers out of the bank’s office in Palo Alto, Calif., the panel of appellate judges wrote in its 61-page decision. In December 2000, Mr. Quattrone wrote a 22-word e-mail endorsing an earlier e-mail whose subject line was “Time to clean up those files.”

The Court of Appeals decided that U.S. District Judge Richard Owen had incorrectly instructed the jury that it could convict Mr. Quattrone even in the absence of proof that he knew the documents in question had been subpoenaed by the government.

“More is required; a defendant must know that his corrupt actions are likely to affect the proceeding,” the panel of appellate judges wrote. Without that proof, all that remained was “a barebones liability crime,” the judges wrote.

“For over three years during this difficult ordeal, I have held my head high knowing I was innocent and never intended to obstruct justice,” Mr. Quattrone said in an e-mailed statement.

His lawyer, Mark Pomerantz, could not be reached for comment.

The appellate judges also questioned Judge Owen’s decision during the trial to limit Mr. Quattrone’s testimony at times to “yes” or “no” answers.

In an unusual move, the court ordered that a different judge hear the next case, if there is to be one.

Mr. Quattrone had been sentenced to 18 months in prison after he had been convicted of three counts. He was also fined about $90,000. He has been free, pending yesterday’s decision.