While authorities didn't identify Ashley Biden or the organisation that paid, the details of the investigation have been laid out in court filings and public statements from Project Veritas.
Ashley Biden was moving out of a friend's Delray Beach, Florida, home in spring 2020 when she stored the diary, tax records, a digital device with family photos, a cellphone and other items there, prosecutors said in a court filing.
They said Harris then moved into the same room, stole the items and got in touch with Kurlander, who enthused in a text message that he would help her make a "ton of money" from it, adding an expletive before "ton".
He ultimately contacted Project Veritas, which asked for photos of the material and then paid for the two to bring the diary and photos to New York, prosecutors said.
Project Veritas staffers met the two in New York and dispatched them back to Florida to retrieve more of Ashley Biden's items from the home, which they did and turned the material over to a local Project Veritas worker, who brought it to New York, prosecutors said.
The group paid the two $20,000 apiece, prosecutors said.
Project Veritas, which identifies itself as a news organisation, is best known for conducting hidden camera stings that have embarrassed news outlets, labour organisations and Democratic politicians. Founder James O'Keefe has cast the organisation's methods as part of a long tradition of journalists using hidden cameras or subterfuge to uncover wrongdoing.
"Project Veritas' news gathering was ethical and legal" in the diary affair, the group said in a statement. The organisation has said that it turned the journal over to law enforcement after receiving it from "tipsters" who maintained that it had been abandoned in a room.
"A journalist's lawful receipt of material later alleged to be stolen is routine, commonplace and protected by the First Amendment," Project Veritas added.
Neither Project Veritas nor any staffers have been charged with a crime.
The FBI searched the group's New York offices and the homes of some of its employees as part of the investigation. A court in New York appointed a former federal judge to review material that was seized in those searches, so as to ensure that investigators couldn't look at material protected by journalistic or attorney-client privileges.
Generally, media organisations aren't culpable for receiving material that might have been stolen, if they weren't involved in the theft. But there can be criminal liability for orchestrating theft and then knowingly paying for stolen material.
"There is no First Amendment protection for the theft and interstate transport of stolen property," the US attorney's office wrote in a court filing last year.
O'Keefe has said that Project Veritas ultimately did not publish information from the diary because it could not confirm it belonged to Ashley Biden.
He added that there was "no doubt Project Veritas acted appropriately at each and every step".
