Top career officials at the Department of Homeland Security’s (DHS) office of the inspector general (OIG) tried to alert Congress in April that Secret Service texts from the time of the January 6 Capitol attack had been erased, but their efforts were nixed by its leadership, documents show.

The officials inside the inspector general’s office – the chief watchdog for the Secret Service – prepared a memo that detailed how the Secret Service was resisting the oversight body’s review into January 6, and delayed informing it about the lost texts.

But after the memo was emailed to the DHS inspector general Joseph Cuffari’s chief of staff, its contents were never seen again, and the disclosure about the erased text messages was never included in Cuffari’s semi-annual report to Congress about oversight work.

The revelation shows that the Secret Service only admitted texts from January 6 were lost months after they were requested by the inspector general’s office, and that Cuffari might have violated federal law in not reporting the matter in the report to Congress.

As noted in the memo, obtained by the Project on Government Oversight and reviewed by the Guardian, the Inspector General Act of 1978 required Cuffari to report “significantly delayed access to information, including the justification of the establishment for such action”.

The circumstances around the erasure of the Secret Service texts have become central to the congressional investigation by the House January 6 select committee, as it examines how agents and leaders planned to move Donald Trump and Mike Pence as violence unfolded at the Capitol.

The Secret Service is a division of DHS, and the chairman of the select committee, Bennie Thompson, in recent weeks has escalated the loss of the texts with the secretary of the Department of Homeland Security, Alejandro Mayorkas, according to sources familiar with the matter.

Thompson has spoken with Mayorkas at least twice, the sources said, and the secretary has deputized an attorney in the DHS counsel’s office to oversee the transfer of materials from the agency to Congress, as investigators examine whether the texts can be reconstructed.

The memo – approved by the DHS office of counsel, the office of investigations, as well as the office of inspections – is particularly significant because it amounted to a compendium of efforts by the Secret Service to seemingly stymie the review.

“Secret Service has resisted OIG’s oversight activities and continued to significantly delay OIG’s access to records, impeding the progress of OIG’s January 6, 2021 review,” the memo said.

Secret Service interviewees, the memo said, regularly indicated that they would not provide documents to the DHS inspector general’s office unless they first went through an internal review, a move potentially in violation of the Inspector General Act.

The memo also noted that on multiple occasions, when the Secret Service produced documents months after they were requested, they contained redactions. The Secret Service did not indicate who approved or applied the redactions or why they were made, the memo said.

Finally, career officials inside the DHS inspector general’s office wrote, the Secret Service claimed they could not access crucial texts from January 6 because of an April 2021 phone system migration that wiped all data from the devices of agents.

The memo was sent to an office overseen by Cuffari’s chief of staff, Kristen Fredericks, on 1 April, according to materials reviewed by the Guardian, so that it could be included in the DHS inspector general’s report to Congress – only for it to be excluded.