The revelation came about on Friday, when FBI agent Jeff Pfeiffer took the stand at a federal court hearing in Alexandria, Virginia, to offer his remarks on the legality of the May 2017 locker raid.
Once on the stand, Pfeiffer stated that he became aware of Manafort's storage locker "either through my investigative efforts" or through an April 2017 meeting between reporters and federal investigators. Pfeiffer added that a reporter had mentioned at the get together that the locker existed, but Pfeiffer wasn't 100 percent sure whether it was the first time it had been mentioned, Politico reported.
Though critics of the April meeting have suggested it created a moment for those involved in the investigation to leak information to the press, Pfeiffer stressed that it was simply a chance for federal agents to see what the reporters had dug up.
When asked by prosecutor Uzo Asonye how federal officials responded to questions from journalists about the probe, Pfeiffer said a "no comment" was typically given.
During his 20 minutes on the stand, the federal agent went on to recall that some six weeks after the meeting, he got in touch with one of Manafort's assistants, Alexander Trusko, who later gave him permission and a key to gain entry to the locker, Bloomberg reported. Trusko was the signer on the lease of the locker.
With a search warrant in hand the following day, Pfeiffer collected the majority of the locker's contents.
Pfeiffer's time at the hearing came to an end when US District Court Judge TS Ellis III called for a recess, allowing defense attorneys to examine a binder they'd been given by prosecutors, according to Politico.
Manafort, who was not present at the hearing, is arguing in this case that the evidence was obtained illegally, as only he had the right to allow Pfeiffer access to the locker. Ellis has not yet offered his judgement on the matter.
Manafort is also facing a July 25 trial in Alexandria on charges of bank fraud, tax evasion and failing to report foreign banks accounts. The 69-year-old is also scheduled to appear in Washington on September 17 on charges of money laundering, failure to register as a foreign agent and witness tampering.
The former Trump campaign chairman is currently being held at the Northern Neck Regional Jail in Warsaw, Virginia.