Federal prosecutors in the District said they are exploring whether a D.C. police department computer glitch resulted in evidence issues that may have affected thousands of cases.

In a letter sent Monday to defense attorneys, U.S. Attorney Ronald C. Machen Jr. said some information recorded by officers investigating crimes was inadvertently omitted from police reports. Those reports, which may include witness accounts or evidence forms, are given to defense attorneys.

“It was possible that in pending and past cases, [the police department] was in possession of information that should have been disclosed to the defense and had unwittingly failed to provide that information,” Machen said in the letter. He said the problem dates back to 2012.

Machen said his office began reviewing cases over the weekend, focusing first on cases that are headed to trial or sentencing in the coming days. As early as Monday, prosecutors began handing stacks of newly recovered documents to defense attorneys.

In the letter, Machen characterized the missing information uncovered so far as “minimal in quantity.” In most instances, he said, the details had been disclosed to the defense through other means or were consistent with “other proof” presented by prosecutors. It is unclear how many cases could be affected.

But defense attorneys argued it was unclear what information was left out and questioned why prosecutors — and not defense attorneys — are deciding whether those details would have changed the defense strategy.

Prosecutors within the U.S. Attorney’s Office say Machen was alerted late last week and ordered an audit over the weekend of current cases.

The ultimate impact will depend on how relevant the omitted details are to the cases.

Julia Leighton, general counsel for the District’s Public Defender Service, said the disclosure “called into question the fairness of the trials.” In the letter, Leighton said, prosecutors “raise more questions than they answer about the scope and the nature of the problem.”

Defense attorney Danny Onorato said it was “astonishing” that D.C. police did not have safeguards in place to ensure that data was accurate and complete. “One can only hope that no one was wrongfully convicted as a result of this mishap.”

D.C. Police Chief Cathy L. Lanier declined to comment. Her spokeswoman said in a statement that the department has updated reports and that employees are using printouts of them “to ensure that all information captured in the system is reflected on those hard copies.”

Karl A. Racine, the District’s attorney general, said his office would review all that office’s closed cases dating back to Jan. 1, 2012. In a letter Tuesday to Lee F. Satterfield, chief judge of D.C. Superior Court, Racine said his office would “make the appropriate disclosures” to defense attorneys.

The problem stems from a computer program known as I/Leads, which has been in use by D.C. police since September 2012. Authorities said some of the information that officers included as they filled out reports failed to download into the final version.

The issue was discovered during a case handled by the Office of the Attorney General, when a police officer insisted during testimony that he had included certain details in his report, but they were not in the final version.

In a statement, spokesman Bill Miller said the U.S. Attorney’s Office was working with D.C. police to fix the problem.

“We are working closely with the police department to resolve this issue and move forward with our shared goal of making sure that the innocent are not wrongfully prosecuted and that the criminals who harm our community are rightfully held accountable for their actions,” Miller said.

Hours before alerting defense attorneys of the missing information, Machen announced he was resigning as the District’s U.S. attorney. Officials within the office said Machen’s resignation was not connected to problem with the reports.

The disclosure comes just weeks after federal prosecutors said they were reviewing hundreds of cases as a result of what they viewed as “critical errors” in how the District’s Department of Forensic Sciences laboratory handled the analysis of DNA evidence. Prosecutors have begun using outside DNA experts and labs to test or evaluate evidence.

Delroy Burton, chairman of the union that represents D.C. police officers, said the computer system has been problematic since it was brought in to merge with the department’s older system in 2012.

The new system was supposed to integrate documents starting with the very first offense report and continuing with witness interview transcripts, evidence forms, and search and arrest warrants.

Spencer S. Hsu contributed to this report.