Members of the House Select Committee on Benghazi interviewed their 98th witness Thursday as they work to wrap up their nearly two-year investigation before the summer.

The closed-door interview of Rear Admiral Richard Landolt, the former director of operations for U.S. Africa Command, came days after Democrats on the committee released a letter from a Pentagon official that criticized the volume of the panel's requests for documents and witness interviews.

Committee Democrats argued the letter was further proof that the probe had "reached a new level of desperation." However, the Defense Department official who authored the April 28 letter has political ties to Democrats, leading to speculation that its release was coordinated with the minority.

The select committee also received more than 400 pages of records from the State Department Thursday in response to a request originally sent in November 2014. Congressional investigators filed a subpoena for the documents in March 2015 after the agency ignored the request.

The new records include personal emails from top Hillary Clinton aides Huma Abedin, Cheryl Mills and Jake Sullivan, committee Republicans said.

Among the mix of private and official emails was new information about how Clinton wanted to take credit for certain aspects of Libya policy, as well as internal staff discussions sent the day before the Benghazi attack. Those talks focused on a protest that had broken out in Cairo over an inflammatory video.

A series of official emails included in the new production may shed new light on the Accountability Review Board, a State Department panel tasked with investigating the agency from within that has been accused of soft-pedaling blame for security failures.

While select committee Republicans have taken fire for the cost and duration of the Benghazi investigation, the majority has pointed to the administration's slow and often deliberately secretive responses to committee requests as the reason behind the length of the probe.

For example, a classified binder of documents provided to the committee by the National Security Agency Friday morning was first requested in April 2015. Various federal agencies have left many witness and document requests to gather dust for months as Democrats lay blame on Republicans for dragging out the investigation.

The Benghazi panel has absorbed more blows as the presidential election draws closer. However, Chairman Trey Gowdy has insisted Clinton is only one aspect of a comprehensive investigation that will focus on what went wrong before, during and after the terror attack — not on the Democratic front-runner's involvement.

After nearly two years of work, congressional investigators are preparing to publish their highly anticipated report before their self-proclaimed deadline before summer, which technically begins next month.

The panel plans to release transcripts from what will ultimately be more than 100 witness interviews at the conclusion of the investigation. However, administration officials must comb through each one and redact potentially sensitive information before the transcripts can be made public, a process that is presently underway.

Seventy-five of the witnesses questioned by the committee to date have never before been interviewed by Congress.