A lawyer for former star investment banker Frank Quattrone (search) asked a federal appeals court Tuesday to toss out his conviction, citing unfair and confusing instructions given to the jury.

Quattrone, one of the biggest Wall Street names of the dot-com boom, was found guilty last year of obstructing a federal stock investigation by endorsing an e-mail to his colleagues encouraging them to destroy files.

His lawyer, Mark Pomerantz, told the 2nd U.S. Circuit Court of Appeals that trial judge Richard Owen gave unfairly broad instructions to the jury.

For example, the judge told jurors they needed to find that Quattrone directed workers to destroy files that were called for in a federal grand jury subpoena issued to his bank, Credit Suisse First Boston (search).

Pomerantz argued jurors should have been told that they could not find Quattrone guilty of obstruction unless they found that he knew the documents he wanted destroyed were the subject of the subpoena.

"You need to know that your conduct will have an impact on what the grand jury hears," Pomerantz said.

David Anders, who prosecuted the case for the government, pointed out another part of the jurors' instructions required them to find Quattrone acted with corrupt intent.

"There was no way for this jury to find that Mr. Quattrone had acted corruptly ... without concluding that he knew or was likely to know that these documents are going to get to the grand jury," Anders said.

Quattrone was convicted based on a 22-word e-mail he sent to CSFB subordinates on Dec. 5, 2000, encouraging them to follow a colleague's recommendation to "clean up" their files.

At the time, federal investigators were looking into how the bank had allocated shares of hot initial public offerings of stock. No charges were brought in the probe, and the bank paid a $100 million civil settlement.

Quattrone, 49, was sentenced to a year and a half in prison, making him the most prominent Wall Street figure since junk-bond king Michael Milken (search) to face time behind bars.

The trial judge initially ordered him to report to prison in October 2004, but the appeals court allowed him to remain free while it considers his appeal.

One judge on the three-judge appeals court panel Tuesday also questioned whether Anders went too far in cross-examining Quattrone at his second trial in April 2004.

At the time, Anders questioned whether Quattrone, acting on behalf of CSFB, had struck a deal in 2000 — undisclosed to investors or regulators — to collect $2 million in fees from Research in Motion executives, who did business with the bank.

Quattrone's lawyers say the line of questioning was irrelevant and could have biased the jury against their client.

One of the three judges, Richard Wesley, said to the prosecutor that, while lawyers routinely push the envelope, "You really blew the side of the envelope out, didn't you?"

"Respectfully, Your Honor, no," Anders replied.