Documents obtained by ABC News show at least four individual Sanders staffers accessed Clinton voter data and saved the data into folders they created.
Two staffers were readily identifiable from the documents: National Data Director Josh Uretsky, who has been fired by the campaign, and his deputy.
The Clinton campaign learned of the breach on Wednesday, according to a Democrat familiar with the breach.
An audit trail that was maintained by the database company NGP VAN appears to show that four Sanders staffers conducted 25 specialized searches of the Clinton campaign's data, including queries for "turnout" and "primary priority" in a 40-minute window.
According to the documents, the Sanders staffers who accessed the voter data appeared to create folders that they then shared with each other and started saving lists to. They ran searches on a number of early voting states, including Iowa, New Hampshire and South Carolina.
The DNC suspended the Sanders campaign's access to the system, according to a press release, and will re-enable the campaign's access once "the DNC is provided with a full accounting of whether or not this information was used and the way in which it was disposed."
Sanders campaign manager Jeff Weaver told ABC News that "It's unfortunate that your source for the logs did not see fit to share them with us so we can do our own internal review -- a review that is hampered by the DNC's improper actions keeping us from our databases. We have fired one employee and are looking into the actions of others. But the DNC and the vendor are playing keep away with the information we need. None of this justifies the DNC's confiscation of our own data."
Weaver insisted that no data "was exported in a way that could be used by anybody" in a press conference Friday, and implied that the DNC is in cahoots with the Clinton campaign. He called the suspension “unacceptable" and accused the DNC of “stealing” data from the Sanders campaign.
“This is unacceptable. Individual leaders of the DNC can support Hillary Clinton in any way they want, but they are not going to sabotage our campaign," Weaver said. "We are announcing today if the DNC continues to hold our data hostage and continues to attack the heart and soul of our grassroots campaign, we will be in federal court this afternoon seeking immediate relief. What is required here is a full and independent audit of the DNC's mishandling of this data, and its security from the beginning of this campaign to the present. In this case it looks like they are trying to help the Clinton campaign.”
Weaver blasted the DNC for locking them out of their data and argued that by doing so the DNC was interfering with the campaign's ability to investigate.
"The DNC, by their own actions, is hindering our ability to do an investigation," Weaver said.
He did acknowledge some wrongdoing by the campaign. “In the heat of these campaigns, sometimes young people make misjudgments," Weaver admitted.
Without access to voter data, Sanders' field organizing and campaigning efforts could be affected six weeks before the first primary votes are cast in the Iowa caucuses.