Employees at the Denver-based IT company that Hillary Clinton hired in 2013 to manage her private email network expressed concern that they were “covering up” something “shady.”

That’s according to a letter sent Monday by Wisconsin U.S. Sen. Ron Johnson to Austin McChord, the CEO of Datto Inc., a Connecticut-based computer cloud storage company.

According to Johnson, who chairs the Senate Homeland Security and Government Affairs Committee, a Clinton family company called the Clinton Executive Services Corp. hired the Denver company, Platte River Networks, on May 31, 2013 to oversee Clinton’s private email network. Platte River in turn hired Datto to create a virtual backup server of Clinton’s emails.

During most of her tenure as secretary of state, Clinton used a server that she housed in her Chappaqua, N.Y. home. But data from that device was transferred to a Datto server controlled by Platte River, which housed the new hardware at a New Jersey data center.

The FBI seized that server in August after the Intelligence Community inspector general discovered that Clinton aides had sent her two “top secret” emails. Clinton has claimed that she did not send or receive classified information on her server.

According to Johnson’s letter, which was obtained by The Daily Caller but first reported by McClatchy, the Clinton Executive Services Corp. twice instructed Platte River to reduce how much email data was being stored during each server backup.

That request caused concern among Platte River employees, according to emails Johnson cites.

One Platte River employee wanted to search the company’s email archives for emails Clinton Executive Services Corp. sent in October or November 2014 and then again this February related to the request records draw-down.

“Any chance you found an old email with their directive to cut the backup back in Oct-Feb. I know they had you cut it once in Oct-Nov, then again to 30days [sic] in Feb-ish. If we had that email, we are golden,” the employee wrote to a colleague on Aug. 19.

The email was sent after Platte River had been identified in news articles as Clinton’s IT service provider. That revelation caused the small firm a major headache. The company hired an outside PR firm to deal with media requests after a company attorney stated, apparently falsely, that no backups of Clinton’s emails existed.

The employee’s email indicates that the company wanted to ensure that it would not be blamed for any perceived cover-up related to Clinton’s emails.

“Wondering how we can sneak an email [to Clinton Enterprise Services] in now after the fact asking them when they told us to cut the backups and have them confirm it for our records,” the employee wrote, adding: “Starting to think this whole thing really is covering up some shaddy [sic] shit.”

“I just think if we have it in writing that they told us to cut the backups, and that we can go public with our statement saying we have had backups since day one, then we were told to trim to 30days [sic], it would make us look a WHOLE LOT better,” the employee added.

A footnote to Johnson’s letter notes that a Platte River determined that the request to cut the number of days for the backups was communicated by phone.

Johnson questions the timing of the decision to reduce the backup time.

“It is unclear why Secretary Clinton’s representatives apparently directed [Platte River Networks] to reduce the backup time period of her emails around the same time period or in the months following the State Department’s request,” Johnson writes to McChord.

Johnson’s letter also provides evidence that Datto may have copies of Clinton emails, raising hopes that the records could be compared to the 55,000 pages of documents Clinton turned over in December. Clinton has said that she has turned over all of her work-related emails, though many observers have questioned the claim.

The FBI has already reportedly recovered some data from Clinton’s server, despite claims she and her attorney have made that no information exists on the hardware.

According to Johnson’s letter, Platte River employees expressed “confusion” after they discovered that Clinton’s server “was potentially being sent to Datto’s off-site location.”

But according to Platte River, Clinton’s emails were only supposed to be backed up at the server in New Jersey, not off-site.

After that discovery, one Platte River employee sent a terse email to Datto on Aug. 6 stating “[t]his is a problem. This data should not be stored in the Datto Cloud.”

According to Johnson, Datto’s servers had backups of Clinton’s emails dating back to June 2013.

Because of the security implications involved in handling Clinton’s emails, Platte River instructed Datto to not delete the data. They also sought to work with Datto “to find a way to move the saved information…back to Secretary Clinton’s private server.”

This article has been updated with additional information.

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