A federal judge ruled Friday that the Justice Department unlawfully accessed evidence central to its case against former FBI director James B. Comey, delivering what could be a death blow to President Donald Trump’s efforts to reindict one of his most prominent perceived rivals.

U.S. District Judge Colleen Kollar-Kotelly ordered the FBI to return emails and other electronic communications it seized from Comey confidant Daniel Richman roughly five years ago as part of a separate investigation that did not result in charges.

Those records had formed the backbone of the case the Justice Department filed against Comey in September, and without them prosecutors maintained they were “effectively enjoined … from investigating or prosecuting Comey.”

Kollar-Kotelly faulted authorities for failing to obtain new search warrants before using the old Richman material as part of the Comey investigation. She described that lapse as a fundamental violation of Richman’s rights.

“When the Government violates the Fourth Amendment’s prohibition on unreasonable searches and seizures by sweeping up a broad swath of a person’s electronic files, retaining those files long after the relevant investigation has ended, and later sifting through those files without a warrant to obtain evidence against someone else, what remedy is available to the victim of the Government’s unlawful intrusion?” she wrote.