The nomination of a former prosecutor to become secretary of homeland security could reopen questions about his response to allegations of wrongdoing by a longtime government informant and reputed organized-crime associate.

The claim that the nominee, Michael Chertoff, failed to rein in the informant, Stanley Myatt, was first raised in May 2003 when the ex-prosecutor was up for confirmation to the federal bench. A dispute over how to pursue the assertions, made by a conservative legal watchdog group, Judicial Watch, led six Democrats to vote “present” on the nomination in the committee.

According to Judicial Watch, Myatt worked as an informant for the FBI and other government agencies for three decades. The group said Myatt used his relationship with the government to bilk seven publicly traded companies of millions of dollars and to intimidate business associates.

“Myatt’s an embarrassment for the Justice Department,” the president of Judicial Watch, Thomas Fitton, said. “He’s one of these informants out there doing these wrong things that they should have known about but they didn’t do anything about.”

Myatt, 64, appears to crave a low profile, but his background was detailed in an article published in Vanity Fair magazine just a few weeks after Judge Chertoff was confirmed to the Third Circuit Court of Appeals. At a 2001 racketeering trial, a former boss of the Philadelphia mob, Ralph Natale, said Myatt helped arrange contacts between local mafia figures and members of the Russian mafia based in South Florida. “He made a big connection with the Russian mob,” Natale said. He also called Myatt a “Wall Street scam man.”

Also in 2001, a veteran marijuana trafficker, James Pritchett, was captured on tape in a Florida parking lot attempting to hire a man to kill Myatt. Pritchett was convicted of attempted murder, but Myatt reportedly did little to cooperate with police.

Myatt did not return phone calls to his home and office in Miami seeking an interview for this story. A lawyer who has represented Myatt, David Berman, declined to comment.

According to public records, Myatt has also attempted to break into the music business, by starting a rap record label. He also founded a company, Organized Crime Family Inc., that planned to create an animated series about the mafia. Myatt is currently part-owner of a publicly traded telemarketing company, Epixtar.

According to Judicial Watch, much of Myatt’s contact with the government was through the federal government’s organized-crime strike force in New Jersey. From 1990 to 1994, Judge Chertoff served as chief federal prosecutor for the Garden State. During the three preceding years, he was the number-two prosecutor at that office.

Staff members of the Judiciary Committee conducted a brief inquiry into the allegations and dismissed them. “There is no credible evidence linking Mr. Chertoff with any of the wrongdoing alleged by Judicial Watch,” the then-chairman of the committee, Senator Hatch of Utah, and the ranking Democrat, Senator Leahy of Vermont, said in a written statement.

According to sources familiar with the inquiry, Judge Chertoff said that while in New Jersey he never dealt with any matter related to Myatt.

It is unclear, however, whether the Senate inquiry, which lasted only a few days, explored the response of officials of the Justice Department at Washington to the claims about their allegedly wayward informant. According to Mr. Fitton, Myatt’s activities were brought to Judge Chertoff’s attention while he served at Washington as head of the department’s Criminal Division.

The information about Myatt was offered to Justice as part of an effort to obtain immunity for a California businessman, Peter Paul, who is facing stock-fraud charges in connection with the collapse of an entertainment firm, Stan Lee Media.

“We went to Chertoff in 2001 about the whole universe of Peter’s information,” Mr. Fitton said. “Chertoff said he would take personal interest in this case.”

A White House spokesman, Kenneth Lisaius, noted that when Judge Chertoff’s judicial nomination came to the Senate floor, it passed by a vote of 88 to 1.”They found those charges to be baseless,” he said.

Mr. Lisaius declined to discuss the allegations in detail, but he suggested Judge Chertoff’s current nomination faces smooth sailing.

“Judge Chertoff has been confirmed three times by the Senate for important federal positions,” the spokesman said.

Given the source of the allegations about Judge Chertoff, the senators’ apparent skepticism is understandable. Paul is a three-time convicted felon who departed America for Brazil as Stan Lee Media fizzled out. He is under indictment at California and Long Island on charges that he and cohorts engaged in a scheme to artificially inflate the company’s stock price.

The Justice Department has since concluded, however, that one of Paul’s most significant claims was true. Paul, who bankrolled a gala fund-raising event at Beverly Hills for Senator Clinton’s 2000 campaign, asserted that the campaign grossly understated the event’s expenses.

Last week, a federal court unsealed an indictment charging Mrs. Clinton’s national finance director, David Rosen, with four felony counts for causing false reports to be filed with the Federal Election Commission. The indictment alleges that while the campaign reported the cost of the fund-raising affair to be about $400,000, Mr. Rosen knew that the true cost was about $1.2 million.

Through his attorney, Mr. Rosen has denied the charges. A lawyer for Mrs. Clinton, David Kendall, predicted the former finance official will be cleared.

The Justice Department said other officials on the campaign of Mrs. Clinton, who at the time was first lady, are cooperating with the investigation.

While the unsealing of the indictment may bolster Paul’s credibility somewhat, it also appears to decrease the likelihood that the Senate will undertake a more thorough inquiry into the claim that, under Judge Chertoff’s watch, the Justice Department allowed its informants to act with impunity.

Any attention to Myatt’s claims could now be politically costly to both Democrats and Republicans. Trouble for Judge Chertoff’s nomination would be embarrassing to the White House. Questions about Paul and Myatt could irk Democrats by drawing attention to the alleged financial malfeasance during Mrs. Clinton’s 2000 race.

“There’s going to be a mutual reason not to pursue this Myatt issue,” Mr. Fitton said. He said his organization does not oppose Judge Chertoff’s nomination but would like to see the informant issue aired publicly. “Maybe they did do an adequate investigation,” he said.

The senators who voted present on the Chertoff appeals court nomination before the Judiciary Committee were Mr. Leahy, Senator Feinstein of California, Senator Schumer, Senator Durbin of Illinois, Senator Edwards of North Carolina, and Senator Kennedy of Massachusetts.

At that hearing, Mrs. Feinstein pressed to delay the vote on the nomination so that the Myatt allegations could be explored. “If we set the precedent by just blithely passing someone out and not investigating this claim, I don’t think we’re doing our jobs,” she said.

Ultimately, the committee agreed to vote first and then look into Judicial Watch’s assertions.

All those who voted present in the committee voted in favor of Judge Chertoff’s nomination on the Senate floor a few weeks later, except for Mr. Edwards, who was absent.

Mrs. Clinton cast the lone vote against Judge Chertoff. She later said she did so to express her dissatisfaction with his treatment of young members of the White House staff who were called as witnesses when he served as chief counsel to the Senate’s investigation of the Whitewater land deal.