The FBI on Sunday said it "failed to preserve" five months of text messages involving a senior agent who was taken off Special Counsel Robert Mueller’s investigative team following a report he made derogatory comments about President Donald Trump, The Washington Post reports.

The revelation came after the Justice Department turned over additional text messages to Congress involving Peter Strzok, a veteran counterintelligence agent who also worked the Hillary Clinton email case. He was discharged from Mueller's team after Mueller learned that he had traded politically charged text messages — many anti-Trump in nature — with an FBI lawyer who was also detailed to the group. The lawyer, Lisa Page, left Mueller's team before the text messages were discovered.

"The Department wants to bring to your attention that the FBI’s technical system for retaining text messages sent and received on FBI mobile devices failed to preserve text messages for Mr. Strzok and Ms. Page," said the letter, signed by assistant attorney general for legislative affairs Stephen Boyd.

Citing "misconfiguration issues related to rollouts, provisioning, and software upgrades that conflicted with the FBI’s collection capabilities," Boyd explained that "data that should have been automatically collected and retained for long-term storage and retrieval was not collected."