A government watchdog accused the U.S. Secret Service of erasing texts from Jan. 5 and 6, 2021, after his office requested them as part of an inquiry into the U.S. Capitol attack, according to a letter sent to lawmakers this week.

Joseph V. Cuffari, head of the Department of Homeland Security's Office of Inspector General, wrote to the leaders of the House and Senate Homeland Security committees indicating that the text messages have vanished and that efforts to investigate the Jan. 6, 2021, attack were being hindered.

"The Department notified us that many U.S. Secret Service (USSS) text messages, from January 5 and 6, 2021 were erased as part of a device-replacement program," he wrote in a letter dated Wednesday and obtained by The Washington Post. The letter was earlier reported on by CNN.

Cuffari emphasized that the erasures came "after" the Office of Inspector General requested copies of the text messages for its own investigation, and signaled that they were part of a pattern of DHS resistance to his inquiries. Staff members are required by law to surrender records so that he can audit the sprawling national security agency, but he said they have "repeatedly" refused to provide them until an attorney reviews them.

"This review led to weeks-long delays in OIG obtaining records and created confusion over whether all records had been produced," he wrote, and offered to brief the House and Senate committees on the "access issues."

The Secret Service's text messages could provide insight into the agency's actions on the day of the insurrection and possibly those of former president Donald Trump. A former White House official last month told the House select committee investigating the assault on the Capitol that Trump knew his supporters were armed, wanted to lead the mob to the Capitol and physically assailed the senior Secret Service agent who told him he could not.

Cuffari, nominated by Trump in 2019 and confirmed by the Senate, has faced significant criticism since he took over the office. His first-year audits plummeted to historic lows, he clashed with Immigration and Customs Enforcement over the veracity of an inspection of a detention center, and he blocked investigations into the Secret Service's handling of George Floyd protests in Lafayette Square and the spread of the coronavirus in its ranks, documents show.

The OIG's office is under investigation by the Council of the Inspectors General on Integrity and Efficiency (CIGIE), an independent entity in the executive branch, for undisclosed allegations of misconduct, according to an internal email circulated to the office in January.

The nonprofit Project On Government Oversight (POGO), an independent watchdog, has called on President Joe Biden to remove Cuffari.

Cuffari's office did not respond to requests for comment on Thursday, and DHS had no immediate comment on his allegations.

A person briefed on the Secret Service's reaction to Cuffari's letter said the agency rejects his characterizations that they eliminated or deleted records after Cuffari's office requested them.

According to two people briefed on the documents request, the Secret Service began a long preplanned, agencywide replacement of staff telephones to improve communication across the agency in January 2021.

It wasn't until sometime in February 2021 that Cuffari's office requested that the Secret Service produce records that centered on Jan. 6 and the days leading up to the attack on the Capitol, seeking internal agency communications, memorandums, emails and telephonic records such as text messages.

By the time of the request, the people said, as many as a third of Secret Service personnel had been given new cellphones.

Most of the replacement program began with staff in Washington offices, and if they did not back up their old text messages, the people said, the information from Jan. 6 and the days before that is lost. That could conceivably include the texts sent and received by former White House deputy chief of staff Tony Ornato and former Trump security detail leader Bobby Engel and other senior leaders in the Secret Service.

This device replacement program, and resulting failure to back up texts, does not appear to affect emails.

The Secret Service has a policy requiring employees to back up and store government communications when they retire old electronic or telephonic devices, but in practice, staff do not consistently back up texts from phones.

A similar issue came up in 2018, when the Justice Department inspector general said he used "forensic tools" to recover missing text messages from two senior FBI officials who had investigated Hillary Clinton and Trump and exchanged notes critical of the president. The missing messages generated criticism when GOP leaders and the president questioned how the FBI failed to preserve them.

Sen. Gary Peters, D-Mich., chairman of the Senate Homeland Security and Governmental Affairs Committee, said lawmakers "need to get to the bottom of whether the Secret Service destroyed federal records or the Department of Homeland Security obstructed oversight."

"The DHS Inspector General needs these records to do its independent oversight, and the public deserves to have a full picture of what occurred on January 6th," he said in a statement. "I will be learning more from the DHS Inspector General about these concerning allegations."

- - -

The Washington Post's Devlin Barrett in Machipongo, Va., contributed to this report.