Last week, the disclosure of a total of five immunity agreements handed out by the Justice Department as part of its investigation of the Clinton email scandal. The extent of the deals and the recipients were surprising, particularly in the failure to previously disclose those deals. As a criminal defense lawyer, I was surprised to see the deals include Cheryl Mills, one of the highest officials accused in the deletion of tens of thousands of emails and the failure to heed warnings over the risk to national security from the use of the Clinton private server. Below is the column.

When FBI Director James B. Comey announced that there would be no criminal charges in the Clinton email scandal, there was an outcry by many who saw glaring contradictions, attempts to destroy evidence, and knowing failures to protect classified or sensitive information. At the time, I acknowledged that Comey’s decision was understandable and, while criminal charges might have been possible, this was not out of bounds of prosecutorial discretion. However, the news this week of a previously undisclosed immunity deal with a top Clinton aide raises serious questions over the handling of the FBI investigation.

The latest recipient of an immunity deal from the Justice Department is one of Clinton’s closest aides and a figure at the heart of the email scandal, Cheryl Mills. She joins two other central figures in benefiting from such deals: former State Department staffer, Bryan Pagliano and tech specialist Paul Combetta. In addition to at least two other immunized witnesses according to the Associated Press, they represent the big three of officials involved in the underlying allegations of Clinton’s potential criminal conduct. Their collective immunization is baffling.

For the Obama Administration, the criminal investigation into the Democratic presidential nominee and its prior secretary of State came with a heightened level of public scrutiny and skepticism. Many doubted that the administration would seriously pursue the Clintons, a family of political royalty in both Democratic and establishment circles. The easiest way for prosecutors to scuttle a criminal case is to immunize those people who are at the greatest risk of criminal indictment. Often prosecutors will avoid immunity deals in favor of offering plea bargains to key players, tying their cooperation against others to reduced sentences. Although a witness can lose an immunity deal by withholding evidence or lying, a witness can undermine cases against superiors by tailoring their accounts or memories to avoid statements showing intent or knowledge.

Before the disclosure of the Mills immunity deal, the two prior deals were curious given the evidence against both Pagliano and Combetta. Pagliano set up the notorious private server and later joined Clinton at the State Department, where various people raised objections to her use of unsecured communications. If Pagliano was problematic, Combetta’s immunity deal was perplexing. Combetta used a product called BleachBit to eradicate evidence of Clinton emails after a telephone conference with Clinton staffers. When he used the product, he admitted that he knew that Congress had issued a subpoena ordering the preservation of the evidence. Then, this month, it was alleged by a “Twitter sleuth” that Combetta, acting under the alias “stonetear,” solicited advice on how to change email records to remove a “VIP’s (VERY VIP) email address.” Either Combetta did not disclose this effort in violation of his immunity deal or the Justice Department effectively removed a serious threat of indictment though the agreement. Despite immunity deals pledging cooperation with all parts of the government, both Pagliano and Combetta have refused to answer questions from Congress, and Pagliano is facing a contempt sanction.

Mills is a participant in key emails and features prominently in allegations of destroyed emails. She was alleged to have been informed repeatedly of the dangers to national security, particularly regarding Clinton’s use of a personal BlackBerry. She was also central in the deletion of tens of thousands of emails that Clinton claimed were purely personal and not work related.

Many of those emails are now known to have discussed official issues and potentially embarrassing disclosures. Mills’ role in the later investigations has also been controversial. Surprisingly, defense attorney Beth Wilkinson agreed to jointly represent various former aides, including not just Mills but Deputy Chief Jake Sullivan, Mills’ deputy Heather Samuelson, and Clinton spokesman Philippe Reines. Wilkinson is a very accomplished lawyer and there is no evidence of unethical acts. However, attorneys rarely represent parties with potential conflicts of interest and the agreement allowed for a single attorney to monitor the consistency of aides in their accounts.

The joint representation of the Clinton aides increased the chance for a uniform account in the controversy. Making this even more concerning is that Mills was allowed by the FBI to sit in on the interviews with Clinton, despite that fact that she was a key witness herself in the investigation. Mills, who is a lawyer, did not hold a legal position at the State Department and should have been excluded from the interviews. Finally, Mills has continuing interests in the election of Hillary Clinton, a development that would place her at the very top of the government.

Of all of the individuals who would warrant immunity, most would view Mills as the very last on any list. If one assumes that there may have been criminal conduct, it is equivalent to immunizing H.R. Haldeman and John D. Ehrlichman in the investigation of Watergate. Mills appears repeatedly at critical moments as one of the most senior figures making decisions or monitoring events, including being informed as Clinton chief of staff of the search for emails by the State Department in response to a Freedom of Information demand in 2012 (three years before the disclosure of Clinton’s use of a private email server). In such circumstances, immunity can amount to impunity. Immunity does not remove the threat of prosecution, but it certainly reduces that threat, while the value of defending prior benefactors or loyalties can remain. Given the overlapping immunity deals, many will now find it unsurprising that Comey did not find evidence of “intentional misconduct or indications of disloyalty . . . or efforts to obstruct justice.”

Comey removed the greatest threat that could have been used to get two underlings to implicate senior officials, and then gave immunity to the senior official most at risk of a charge. In the land of the immunized, the degree of cooperation can sometimes be as difficult to establish as the truth.

Jonathan Turley is the Shapiro Professor of Public Interest Law at George Washington University and a member of USA TODAY’s board of contributors.