Originally Published: 01 AUG 22 15:48 ET

By Whitney Wild and Priscilla Alvarez, CNN

(CNN) -- Key House Democrats have issued a new call for the Department of Homeland Security's inspector general to recuse himself from a probe of missing Secret Service text messages after a CNN exclusive report showed investigators knew for more than a year texts had been erased.

House Oversight Committee Chairwoman Carolyn Maloney and House Homeland Security Chairman Bennie Thompson reiterated their call for Inspector General Joseph Cuffari to step aside in a letter on Monday.

"We are writing with grave new concerns over your lack of transparency and independence, which appear to be jeopardizing the integrity of a crucial investigation run by your office," they said in the letter.

Maloney and Thompson also are demanding transcribed interviews with key DHS IG staffers. CNN first reported that DHS inspector general investigators dropped efforts to recover missing Secret Service text messages in July 2021, a year before Cuffari raised concerns about Secret Service and DHS transparency to congressional oversight committees.

"The Committees have obtained new evidence that your office may have secretly abandoned efforts to collect text messages from the Secret Service more than a year ago," the letter said. "These documents also indicate that your office may have taken steps to cover up the extent of missing records, raising further concerns about your ability to independently and effectively perform your duties as Inspector General (IG)."

The committees are requesting a slate of communications and documents by Monday.

The letter shows a DHS deputy inspector general, Thomas Kait, wrote an email to a DHS senior liaison, Jim Crumpacker, on July 27, 2021, advising DHS investigators were no longer seeking text messages. Kait is one of the staffers the committee wants to interview now.

"Jim, please use this email as a reference to our conversation where I said we no longer request phone records and text messages from the USSS [United States Secret Service] relating to the events on January 6th," the email said, according to the letter.

The letter also confirms CNN reporting that the probe into text messages was reopened in December 2021.

Lawmakers said in Monday's letter that Kait also removed "key language" from a February memo to DHS underscoring the significance of text messages to the inspector general's investigation. The original memo mentioned that most DHS components had not provided requested information and noted text message content is a "critical source of information for the DHS OIG review," but the final version stated the opposite, saying that they had received responses, according to the letter.

"These documents raise troubling new concerns that your office not only failed to notify Congress for more than a year that critical evidence in this investigation was missing, but your senior staff deliberately chose not to pursue that evidence and then appear to have taken steps to cover up these failures," the letter states.