The Justice Department is granting immunity to the former State Department staffer who worked on Hillary Rodham Clinton’s private email server, The Washington Post reported Wednesday night. The move is a sign that the FBI investigation into possible criminal wrongdoing is progressing, the Post reported.A senior U.S. law enforcement official told the Post that the FBI had secured the cooperation of Bryan Pagliano, who worked on Clinton's 2008 presidential campaign before setting up the server in her New York home in 2009.The next step is a likely interview of Clinton herself as the FBI looks to wrap up its investigation in the coming months. Her senior aides also will be sought for interviews.The key question is whether any of the participants knew they were sending classified information in emails, current and former officials said. Another key question will be whether the setup of the server was a scheme to hide information.The inquiry comes against a sensitive political backdrop in which Clinton is the favorite to secure the Democratic nomination for the presidency."As we have said since last summer, Secretary Clinton has been cooperating with the Department of Justice’s security inquiry, including offering in August to meet with them to assist their efforts if needed," Clinton campaign spokesman Brian Fallon told the Post, adding that the campaign is "pleased" Pagliano is now cooperating.Pagliano previously invoked his Fifth Amendment right against self-incrimination.The Justice Department, FBI and Pagliano's lawyer declined to comment.The probe will look what damage would have been done had the confidential information been exposed, the Post reports, adding that while the Clinton campaign has described the investigation as a security review, the Justice Department and FBI have said they are looking into whether a crime was committed."There was wrongdoing," the newspaper quoted a former senior law enforcement official. "But was it criminal wrongdoing?"Attorney General Loretta Lynch told Congress earlier this year that the case is being handled by "career independent law enforcement agents, FBI agents, as well as the career independent attorneys in the Department of Justice" who will follow the evidence, look at the law and "make a recommendation to me when the time is appropriate."The FBI is likely trying to establish whether Clinton and her aides understood the protocols of sending and receiving classified information, former officials told The Post.Clinton has said she did not send or receive information "marked classified" at the time, though hundreds of the emails released through a Freedom of Information Act request are now deemed various degrees of classified and include redactions – in some cases the entire email. Fox News' Catherine Herridge reported on Monday that one of the emails in the final batch released was withheld on request of law enforcement, and that she had received a tip months ago that at least one of them contained information that the senders understood the information was classified at the time.Texas Sen. Ted Cruz on Wednesday called the grant of immunity "an ominous development" for the Clinton campaign."This suggests the investigation is moving to a whole other level, and granting immunity means they'll question this individual and get all the facts of what he did and in particular, what secretary Clinton told him, what her close associates told him, what they knew and instructed, and that suggests that the legal jeopardy is just getting greater and greater," Cruz said on Fox News Channel's "The Kelly File."