PetroTiger ex-CEO Joseph Sigelman wants access to a probe that led to bribery charges against him.

To tackle corporate bribery, the U.S. Department of Justice is increasingly relying on companies to turn over their own bad apples. But one former chief executive is trying to turn the tables, arguing that he should be able to use the results of the corporate investigation that uncovered corruption allegations against him.

The request, argued in a motion filed last week in New Jersey federal court by lawyers for former PetroTiger Ltd. CEO Joseph Sigelman, raises key questions about the confidentiality of independent investigations. In recent years, those internal probes have played a vital role in helping the U.S. Department of Justice bring antibribery cases.

Mr. Sigelman claims that the company’s internal investigation, handled by law firm Sidley Austin LLP, served as the impetus for the Justice Department’s charges that the CEO bribed a Colombian official. The investigation documents could therefore “exonerate him” in the bribery case headed to trial in District Court in New Jersey in January, wrote Mr. Sigelman’s counsel, William Burck of Quinn Emanuel Urquhart & Sullivan LLP.

Sidley Austin says that though it shared some of its findings with authorities, its probe was a private matter protected under attorney-client privilege. The firm is asking the court to deny the request.

Companies often hire outside law firms to conduct internal investigations after they uncover evidence of bribery. Such probes serve an increasing role in enforcement of the Foreign Corrupt Practices Act, a 1977 law prohibiting foreign bribery.

In exchange for a shot at leniency for the company, the outside counsel often turns over its evidence to the Justice Department, which can then use the findings to pursue individual executives.

Given the central role these probes can play in prosecutions, some now question whether the information gathered by these firms should be protected with the same shield of confidentiality granted other attorney work. While the Justice Department has to turn over documents to defense that are part of its own investigation, a spokesman said it doesn’t involve itself in the discovery of outside counsel.

Attorneys who represent companies in these probes say that allowing subpoenas of an outside law firm would have a chilling effect on companies seeking to discover internal wrongdoing.

“On the other hand, the individual defendant, especially in a criminal case, has the need to know what potential trial witnesses have previously said in the event it’s relevant to their defense,” said Kathleen Hamann, a former prosecutor from the Justice Department’s FCPA unit, now a partner at White & Case LLP.

An internal investigation at PetroTiger, a British Virgin Islands-based oil services company that operates in Colombia, led to bribery charges against Mr. Sigelman—who maintains his innocence—and two other executives, co-CEO Knut Hammarskjold and general counsel Gregory Weisman, both of whom have pleaded guilty to bribery charges.

A dispute with PetroTiger’s board over strategy and corporate governance led to the ousting of the three executives by March 2011, according to court documents. PetroTiger then hired Sidley Austin to conduct an internal investigation, during which the law firm uncovered evidence of payments to the wife of a Colombian official at Ecopetrol SA, Colombia’s state-run petroleum company, according to court documents and a former PetroTiger board member.

Sidley reported the payments to the Justice Department and handed over thousands of pages of company documents. Prosecutors say the payments of approximately $333,500 to the wife for “consulting services” was actually a bribe to her husband to win a contract for PetroTiger worth around $39.6 million.

Mr. Sigelman’s counsel argues that Sidley waived its attorney-client privilege “when it divulged the investigation’s findings to third parties, including officials of the United States.”

Sidley says that while PetroTiger’s board hired the attorneys to help conduct an internal investigation, its attorneys are on neither side of the criminal case, and that it shouldn’t have to help Mr. Sigelman in a “fishing expedition” that could cost the firm hundreds of thousands of dollars to wrangle the huge volume of documents.

Experts say that courts have begun to erode the protections over internal probes. “We tell our clients that we will do everything we can to protect that privilege but you can’t be sure what’s going to happen,” said Laurence Urgenson, a partner at Mayer Brown LLP.

In an unrelated defamation case last year, a federal judge in New York ordered the law firm Gibson, Dunn & Crutcher LLP to turn over its interview notes from an internal investigation on financial irregularities at the hedge fund D.B. Zwirn & Co. The judge ruled that Gibson Dunn had in effect surrendered confidentiality over interview summaries and transcripts when it presented part of its findings to the U.S. Securities and Exchange Commission.

Courts have become increasingly uneasy with the claim that attorneys can “selectively waive” attorney-client privilege, said Joseph McLaughlin, an attorney at Simpson Thacher & Bartlett LLP.

“Courts don’t want to approve the practice where a party discloses privileged information when it’s in its perceived interest to share with a third party, then close the door and stop further disclosure when it’s not in their interest,” said Mr. McLaughlin. “The question becomes are they trying to use privilege as both a sword and a shield?”

Write to Joel Schectman at