Some 42 pages of highly redacted documents from the FBI’s criminal investigation into Hillary Clinton’s mishandling of highly classified materials paint a picture of a serious, but flawed investigation hindered by a lack of cooperation, according to a key watchdog group.

The materials, all part of the probe dubbed “Midyear Exam,” included several documents designated as “grand jury material,” indicating the potential seriousness of the investigation that would ultimately be ended by FBI director James Comey in July, then restarted for a brief period in October before being shut down for good.

One redacted exchange reveals a back and forth subpoena response to the FBI from one of Mrs. Clinton’s private attorneys, Katherine Turner, a partner at Washington DC powerhouse firm Williams & Connolly. In the document, Turner agreed to turn over one of Mrs. Clinton’s non-secure Apple iPads and two of her BlackBerrys to the FBI.

But neither smartphone received from the law firm contain SIM cards or Secure Digital (SD) cards, and a total of 13 mobile devices identified by the FBI as potentially using clintonemail.com email addresses were never located by Williams & Connelly.