Associated Press reporters may have tipped off the FBI to a storage unit owned by former Trump campaign manager Paul Manafort that the bureau later raided, an FBI agent testified Friday.

FBI agent Jeff Pfeiffer said the storage unit was mentioned during a meeting with reporters from the Associated Press, who “offered information” they had about Paul Manafort. Officials from the Justice Department’s Criminal Division also attended the meeting, Mr. Pfeiffer said.

Mr. Pfeiffer appeared during a hearing in an Alexandria, Virginia, federal court. He is the first live witness to appear on behalf of the prosecution to blunt defense counsel’s challenges to the storage unit.

Defense counsel have attacked the storage unit search in an effort to have the charges against Mr. Manafort dismissed. He is facing trials in D.C. and Virginia on charges ranging from tax fraud to lying to federal investigators.

He has pleaded not guilty to the charges brought by special counsel Robert Mueller as part of the Russia investigation.

Mr. Pfeiffer could not remember if the journalists were the first to tell him about the storage unit. When asked how he became aware of the unit, he responded, “either through my investigative efforts or through a meeting that occurred with reporters of the Associated Press.”

About a week after the discussion, the FBI met with Alex Trusko, an employee of Mr. Manafort whose name appeared on the storage locker’s lease. The bureau then secured a search warrant and later removed evidence from the locker.

Mr. Pfeiffer said law enforcement wanted to know what the journalists had learned in their investigation, noting that FBI officials generally did not answer the reporters’ questions.

Prosecutor Uzo Asonye asked Mr. Pfeiffer how the Justice Department officials responded to the journalists questions. Mr. Pfeiffer said, “Generally, no comment.”

But when pressed by defense attorney Thomas Zehnle, Mr. Pfeiffer said officials told the reporters, “they had a good understanding” of the information presented.

Lauren Easton, a spokesperson for the Associated Press, described the session as “an effort to get information on stories they were reporting, as reporters do.”

“During the course of the meeting, they asked DOJ representatives about a storage locker belonging to Paul Manafort, without sharing its name or location,” she said in a statement.

The conference between the reporters and Justice Department officials had been previously disclosed, but Mr. Pfeiffer’s testimony offered insight into what may have been discussed during the session.

House Republicans have sought more information on the meeting. Earlier this year, House Intelligence Committee Chairman, Devin Nunes, California Republican, requested the Justice Department turn over records related to the meeting. Of particularly interest to Republicans was the attendance of Andrew Weissman, a top Justice Department prosecutor who later joined special counsel Robert Mueller’s Russia investigation.

Mr. Pfeiffer also recounted the steps he took to obtain a search warrant for the storage locker.

Defense attorneys have asked the the court to toss financial records seized as evidence in the unit’s raid. They have argued that Mr. Trusko did not the authority to allow the FBI into the unit.

Mr. Trusko’s name is on the unit’s lease and he holds a key, prosecutors said. He also signed an FBI search-consent form that authorized the agents to remove items from the locker. All factors that added to the legitimacy of the search, prosecutors argued.

Pfeiffer said he photographed the locker’s contents and then spoke with prosecutors at the Justice Department. The next day the FBI returned with a court-approved search warrant to take a boxes of records and a file cabinet from the unit.

Also on Friday, Judge T.S. Ellis III said he would not dismiss the charges against Mr. Manafort based on allegations prosecutors leaked grand jury information.

Judge Ellis told defense counsel they had one week to file additional motions about the leak, but he would not hold another hearing on the issue.

Kevin Downing, a lawyer for Mr. Manafort, said grand jury leaks and false information about his client had damaged his chances for a fair trial. But Judge Ellis said the leaks did not warrant dismissal of the charges against Mr. Manafort.

“Sanctions for people who made the leaks — that doesn’t affect the trial,” the judge said.

In response, Mr. Downing suggested he may seek a venue change, though he would need to do it by the end of the next week. Mr. Manafort’s Virginia trial is set to begin July 24.

But Judge Ellis also indicted that he would be unlikely to grant such a request, which could move the trial to another courtroom in the Eastern District of Virginia, likely Roanoke or Richmond.

“You better marshal up all your evidence of that,” he said.

Judge Ellis also denied prosecutors’ request to submit a questionnaire to potential jurors, saying it ws unnecessary for the process of picking jurors, known as voir dire.

“All [questionnaires] do is extend the voie dire process,” the judge said, cautioning attorneys from either side not to ask potential jurors who they voted for or which political magazines they read.