The Justice Department searched two locations associated with the conservative group Project Veritas as part of an investigation into how a diary stolen from President Biden’s daughter, Ashley, came to be publicly disclosed a week and a half before the 2020 presidential election, according to people briefed on the matter.

Federal agents in New York conducted the court-ordered searches on Thursday — one in New York City and one in suburban Westchester County — targeting people who had worked with the group and its leader, James O’Keefe, according to two of the people briefed on the events. The investigation is being handled by F.B.I. agents and federal prosecutors in Manhattan who work on public corruption matters, the people said.

After this article was initially published online on Friday, Mr. O’Keefe put out a video confirming that current and former Project Veritas employees had their homes searched on Thursday.

He said the group had recently received a grand jury subpoena and acknowledged that Project Veritas had been involved in discussions with sources about the diary. But he offered a lengthy defense of his group’s handling of the diary, saying that he and his colleagues had been operating as ethical journalists.

“It appears the Southern District of New York now has journalists in their sights for the supposed crime of doing their jobs lawfully and honestly,” Mr. O’Keefe said, referring to federal prosecutors in Manhattan. “Our efforts were the stuff of responsible, ethical journalism and we are in no doubt that Project Veritas acted properly at each and every step.”

Project Veritas did not publish Ms. Biden’s diary, but dozens of handwritten pages from it were posted on a right wing website on Oct. 24, 2020, at a time when President Donald J. Trump was seeking to undermine Mr. Biden’s credibility by portraying his son, Hunter, as engaging in corrupt business dealings. The posting was largely ignored by other conservative outlets and the mainstream media.

The website said it had obtained the diary from a whistle-blower who worked for a media organization that refused to publish a story about it before the election. It claimed to know where the actual diary was located and that the whistle-blower had an audio recording of Ms. Biden admitting it was hers.

The Trump administration Justice Department, then led by Attorney General William P. Barr, opened an investigation into the matter shortly after a representative of the Biden family reported to federal authorities in October 2020 that several of Ms. Biden’s personal items had been stolen in a burglary, according to two people briefed on the matter.

Read Related Also: Honey Boo Boo deletes photo with boyfriend Dralin Carswell after age gap backlash

Mr. O’Keefe said in the video that “tipsters” had reached out to Project Veritas in 2020 to alert them to the existence of the diary, saying that they had stayed in a room that Ms. Biden had recently been in. But Mr. O’Keefe said that his group could not authenticate the diary and made an “ethical” decision to not publish it.

He said that Project Veritas gave the diary to “law enforcement” and attempted to return it to a lawyer representing Ms. Biden, who he said “refused to authenticate it.” Mr. O’Keefe portrayed the investigation as politically motivated, questioning why the Justice Department under Ms. Biden’s father was pursuing the case.

In recent weeks, federal investigators have reached out to at least one person who worked for Project Veritas to question that person about the diary, one of the people briefed on the case said.

Project Veritas has a history of targeting Democratic congressional campaigns, labor organizations, news media and others. The group conducts sting operations, using hidden cameras and fake identities. At one point, Project Veritas relied on a former British spy named Richard Seddon to help train its operatives, teaching them espionage tactics such as using deception to secure information from potential targets.

Flyover Media, the company that owns the website that published the pages from the diary, is registered to the same Sheridan, Wyo., address as Mr. Seddon’s company, Branch Six Consulting International. Mr. O’Keefe, the founder of Project Veritas, was once the president of a company that later registered at the same address.

Project Veritas has a pending libel suit against The New York Times over a 2020 story about a video the group made alleging voter fraud in Minnesota.

Ms. Biden, 40, is Mr. Biden’s youngest child. She has maintained a low profile and attracted far less attention than Hunter Biden, her half brother. In 2019, Mr. Trump withheld military aid from Ukraine at the same time he pressured that country’s president for support in investigating Hunter Biden’s business dealings, leading to Mr. Trump’s first impeachment.