Well, what would Friday be without the latest document dump from the Clinton email investigation? Yesterday afternoon, with the public in distracted anticipation of the coming weekend and Monday s Clinton-Trump debate showdown, the FBI released another 189 pages of interview reports.Along with this document dump comes remarkable news:According to House Oversight Committee Chairman Jason Chaffetz, the limited immunity was granted in order to persuade Ms. Mills to surrender her laptop computer so the FBI could check whether classified information was stored on it.This is very strange. There was no need to grant concessions to Mills. The Justice Department could have required the production of the computer by simply issuing a grand jury subpoena. And had there been any concern that Mills would not cooperate, would destroy the computer, or would  misplace  it (as Team Clinton claims to have misplaced so many Hillary devices), investigators could have applied for a search warrant and seized the computer.In normal cases, the Justice Department does not grant immunity in exchange for evidence when it has lawful power to compel production of that evidence.In a normal case, immunity-from-prosecution never enters into this equation. Immunity is a valuable concession that the Justice Department is only supposed to grant if there is no other way to get the evidence in question. Investigators are not supposed to  pay  for evidence the law empowers them to obtain cost-free. If, for example, a prosecutor surmised that a suspect s hair might match hair recovered at the scene of a robbery, the prosecutor would not offer the suspect immunity from prosecution for the robbery in exchange for the suspect s provision of a hair sample. The prosecutor would issue a subpoena requiring the suspect to provide the grand jury with a hair sample; if there was a match, the grand jury would then indict the suspect for the robbery. As the Associated Press puts it:  By including the emails recovered from the laptops in the immunity agreements, the Justice Department exempted key physical evidence from any potential criminal case against [Hillary Clinton s] aides.  It makes no sense to have done this   unless the Justice Department had already decided it would not prosecute Mills and Samuelson, no matter what the proof showed.Read more: National Review