While the SEC directed its staff for years to purge certain investigative records, other agencies in the United States and abroad that enforce financial laws have instructed that similar documents be kept.

Law enforcement authorities in related lines of work have preserved records of inquiries even if those probes never led to charges against anyone. Regulators and archivists said that the records could be a valuable source of information for investigators probing other cases and could help hold the authorities accountable.

The inspector general at the Securities and Exchange Commission is investigating a long-running SEC policy that calls for purging records obtained in certain inquiries when the cases were closed. The probe was prompted by an internal whistleblower, who said the destruction of documents went on for 17 years.

An SEC spokesman has declined to say why the SEC adopted the policy but has confirmed that it was in place for at least a decade.

The Financial Services Authority, a British counterpart to the SEC, regards its investigative records as “intelligence,” and it orders that they be retained for seven to 15 years, a spokeswoman said.

The policy is essentially “don’t get rid of them because you might need to use them,” FSA spokeswoman Sarah Bailey said. The FSA is one of the world’s premier financial regulators because of London’s role as a global financial capital.

The FBI, which polices some of the same offenses that the SEC does, keeps case files of all criminal investigations for at least 20 years after they are closed, officials said.

Then there are the matters that don’t even rate an FBI investigation — tips that are dismissed with little or no spadework. They are classified into hundreds of subject categories and are deposited in records known as “zero files.”

Several categories of zero files overlap with SEC enforcement, such as insider trading, securities fraud and corporate bribery of foreign officials. FBI spokesman William D. Carter said that the government must keep those files indefinitely, either because the National Archives has not yet set a timetable for their disposal, or has directed that they be preserved forever.

“Being inveterate record keepers, you have to make a notation that something was received, it was looked at, it was determined that there was nothing to it,” Carter said.

The SEC’s practices have been under official scrutiny since an agency whistleblower last year told the National Archives that the SEC was routinely destroying files of inquiries that were closed without any enforcement action or full-blown investigation.

The issue gained wide attention in August when Sen. Charles E. Grassley (R-Iowa) made public an account by the whistleblower’s lawyer. The National Archives has said the SEC did not have authority to dispose of the records.

The whistleblower’s lawyer, former SEC enforcement official Gary Aguirre, has described the practice as part of a dangerously cozy relationship between the SEC and the world it regulates.

Scott A. Hodes, a former FBI lawyer who now handles federal records cases, including one that Aguirre brought against the SEC, said the SEC’s policy “just doesn’t make sense to me.” He added, “If they have to go back and reopen the investigation, they’ve wasted resources.” The agency should keep records at least until the statute of limitations for filing charges has expired, he said.

In Canada, the Ontario Securities Commission, a major regulator, keeps its records for 201 years, spokeswoman Carolyn Shaw-Rimmington said.

The New Brunswick Securities Commission, meantime, keeps electronic copies of investigative records permanently, said Jake van der Laan, director of enforcement.

Van der Laan, who also is chairman of an enforcement committee for Canadian securities regulators, said leads from old cases can help investigators tackle new ones. For example, a sketchy tip about a company trying to lure people into dubious investments could come in handy years later when regulators receive another tip about the same firm, he said.

The Massachusetts attorney general’s office, which like counterparts across the country enforces state securities laws, keeps records of civil investigations for at least six years after final action, according to a document provided by the office. Investigations of consumer complaints are kept for 10 years, the document says.

The U.S. Commodity Futures Trading Commission requires its staff to keep documents from preliminary inquiries for three years, spokesman Steven W. Adamske said.

For investigations that don’t lead to enforcement action, the Federal Trade Commission destroys records five years after the case is closed or when they are no longer needed, whichever is sooner, said Eileen Harrington, the agency’s executive director.

The lawyers handling the cases make those decisions based on the likelihood that the agency will have further use for the information, Harrington said.