On Wednesday news broke that at the end of last month, FBI agents searched one of Paul Manafort’s homes for documents as part of the Russia collusion investigation, directed by special

counsel Robert Mueller. What is the significance of this news, and why didn’t Mueller just obtain the documents by grand jury subpoena? Mueller’s use of a search warrant tells us that he was

able to establish on the basis of evidence, and to the satisfaction of a United States Magistrate-Judge, that there was probable cause to believe that evidence of a specific crime or crimes

existed in the location to be searched. That standard is significantly higher than what is required to obtain a grand jury subpoena, which can be used to obtain any evidence that a grand

necessarily the case. Further, it should be clear that just because Mueller has now reached this stage in the investigation, it does not necessarily mean that Manafort or anybody else will

be ultimately charged with crimes. Now why did Mueller use a search warrant instead of a subpoena, particularly since Manafort’s attorney says that they have been cooperating with the

investigation all along? I can think of four possible reasons for Mueller’s move (none of which are mutually exclusive). First, Mueller and his staff may have decided that, despite the

claims of cooperation from Manafort’s lawyer, Manafort could not be trusted to provide all of the documents requested by subpoena. If Mueller’s team thought that there was any risk that

Manafort would hide or destroy documents, that would be a strong reason to proceed with a search warrant. Second, there may have been a need to move quickly. If Mueller used a grand jury

subpoena, he would have had to give Manafort a reasonable amount of time to comply, and that time might have been further prolonged if Manafort’s lawyer challenged any aspect of the

subpoena. Mueller may have needed the documents quickly in order to identify other lines of inquiry or for purposes of witness interviews, and so may have decided that using a search warrant

would be more expeditious. Third, Mueller may have wanted to avoid any Fifth amendment objections to a grand jury subpoena. Although recipients of grand jury subpoenas demanding documents

ordinarily cannot resist on self-incrimination grounds, because the documents requested were not themselves “compelled” and therefore do not fall within the privilege, there are narrow

situations when witnesses can claim that because the government is engaged in a fishing expedition, compliance with the subpoena requires a testimonial act by the witness which could be

self-incriminating (I wrote about this possibility here in detail in connection with Congressional subpoenas to Michael Flynn). While a search warrant does not simply permit a fishing

expedition, as the government must describe with some particularity the documents it is seeking, it nonetheless forecloses the Fifth amendment objection that Manafort’s lawyer might have

mounted in response to a subpoena. Finally, Mueller’s move may have been in part strategic. He may have wanted to get Manafort’s attention to emphasize the seriousness and advancing nature

of the investigation, all with the hope of securing his cooperation. A predawn search by FBI agents of Manafort’s house could achieve this objective in a way that a grand jury subpoena just

couldn’t. And if Mueller was hoping to send a message, it is one that will likely be received by others in addition to Manafort. If it was not clear already, it should now be plain that

Mueller will use all the investigative tools at his disposal to fulfill the task that he has been assigned. _IMAGE:  GETTY/DREW ANGERER_ FEATURED IMAGE: NEW YORK, NY - JUNE 9: Paul Manafort,

Donald Trump's campaign chairman and chief strategist, leaves the Four Seasons Hotel after a meeting with Trump and Republican donors, June 9, 2016 in New York City. Trump previously

stated he planned to raise one billion dollars, but has since pulled back on his fundraising goal. (Photo by Drew Angerer/Getty Images)