(CNN) Federal prosecutors in New York are scrutinizing tens of thousands of documents relating to Donald Trump's inauguration in a sign that the investigation into the committee's finances is advancing.

The President's Inaugural Committee handed over the cache of documents over the course of several weeks in response to a wide-ranging subpoena seeking documents, records, and communications concerning the inaugural's finances, vendors, and donors sent in February by the US attorney's office with the Southern District of New York. The last set of documents was produced within the last month, people familiar with the matter said.

The end of the document production indicates the investigation is moving into the next stage. Authorities are investigating whether any of the record $107 million in donations for the inaugural was misspent, used to improperly benefit certain individuals, or came from foreign donors in violation of campaign finance laws that prohibit foreign money in US elections, people familiar with the inquiry said.

The ongoing investigation is one of several into Trump's businesses or campaign-related activities the White House is facing on multiple fronts, despite the end of special counsel Robert Mueller's investigation. What prosecutors find could also shed more light on any attempts by foreign governments or businesses to influence the President as the 2020 campaign gears up.

Related: Track the publicly known developments of the sprawling investigations into Trump and Russia.

Prosecutors have interviewed at least one inaugural planner, Stephanie Winston Wolkoff, whose firm, WIS Media, was paid $25.8 million for event production. Wolkoff, a New York City planner who has been involved in events such as the Metropolitan Museum of Art's Costume Institute Gala, known as the Met Gala , was also a close friend of Melania Trump.

The pace and direction of the investigation is unclear. So far prosecutors have not interviewed some of the top finance organizers of the inaugural or asked the Trump Organization for documents, according to people familiar with the investigation. Other people familiar with the investigation say there is no obviously damaging information in the documents.

Representatives for the US attorney's office and inaugural committee declined to comment.

It is not publicly known who else authorities have spoken with. Rick Gates, who was deputy chairman of the inaugural committee, pleaded guilty last year to conspiracy and lying to investigators about unrelated conduct. Prosecutors in Washington have said Gates is continuing to cooperate with the Justice Department. Under his plea agreement he is obligated to cooperate with any federal inquiries.

The federal investigation is not the only one facing the inaugural. State attorneys general from New Jersey and Washington, DC , have also issued subpoenas for records. They are looking at the committee from its status as a nonprofit and whether it violated any laws in how it spent the funds.

Stems from Cohen raid

The federal investigation grew, in part, from a recording prosecutors obtained in the raid of Trump's personal attorney Michael Cohen. Cohen recorded a conversation he had with Wolkoff.

Wolkoff expressed concern in the recorded conversation about how the inaugural committee was spending money, The Wall Street Journal reported.

Wolkoff was subpoenaed by a federal grand jury in Manhattan in October and met with prosecutors, according to people familiar with the investigation. Wolkoff's attorney declined to comment.

The investigation escalated in February when prosecutors sent the subpoena to the inaugural committee, which was led by longtime Trump friend Tom Barrack, for any documents and communications it had related to any "benefits" offered to donors, including "tickets, photo opportunities, and/or small group receptions." Barrack was not named in the subpoena.

It also requires the committee to turn over information about donations made directly to vendors, as well as communications discussing that possibility. And it seeks records related to virtually every donor or donation, attendee at a committee event, piece of paperwork related to the legal requirements attached to donations and even "the possibility of" donations made by foreign nationals.

The inauguration raised a record amount and spent it lavishly on dinners and events, including $1.5 million at the Trump International Hotel in Washington. WNYC and ProPublica , citing emails, reported last year that Wolkoff was concerned about the rates the Trump hotel was quoting.

The subpoena singled out only one person by name: Imaad Zuberi and his investment firm, Avenue Ventures LLC.

It isn't clear what attracted prosecutors to Zuberi, a Los Angeles-based venture capitalist, but the long time donor to Democrats did an about face after the election, piling money into Republican coffers. His company donated $900,000 to the inaugural fund, according to Federal Election Commission records, giving him access to two glitzy dinners.

While Zuberi's donation to the inaugural was large there were 47 individuals and companies that exceeded his contribution.

Zuberi also attended two events that gave him proximity to the president and separately crossed paths with Cohen. In one conversation with Cohen they discussed a potential Manhattan real estate project but it never materialized. Zuberi also has business ties to the Qataris.

In the three months since the subpoena was sent to the inaugural committee Zuberi has not heard from federal prosecutors in New York, his spokesman told CNN. Zuberi is under investigation by federal prosecutors in Los Angeles for tax matters unrelated to the inaugural.