The search warrant can be viewed here, but very quickly I want to draw your attention to this extract from p. 17 of the search warrant:
As the FBI Washington Field Office agent who submitted the affidavit noted earlier in the document (pp. 4–5), “HCS” stands for human intelligence (HUMINT) control system. In other words, the documents marked HCS and observed by the FBI agents who conducted the search and seizure involved information derived from living persons, undoubtedly foreign nationals, who supplied information to the U.S. government.
The compromise of HCS information can lead to the imprisonment or death of the source. I’ll have more to say about this in the near future but I raise it now because of the gravity of the stakes involved.