The FBI's execution of a search warrant at former President Donald Trump's Mar-a-Lago estate in Florida on Monday has prompted questions about the methods federal law enforcement officials use in their investigations.
Here are answers.
How does a federal search warrant work?
The Fourth Amendment of the U.S. Constitution protects against unreasonable searches and seizures. However, federal law enforcement officials may seek search warrants if they believe criminal evidence they seek could be moved, concealed, altered or destroyed if they used less intrusive measures to obtain it.
First, they must swear, under oath, to a series of facts in an affidavit to a federal magistrate judge or district court judge in the area where the warrant is to be executed. The application must show "probable cause" that a crime has been committed and that evidence of the crime is likely to be found at the location to be searched.
In this case, the warrant could have been approved by a judge in Washington, D.C., because the FBI investigation is believed to focus on classified documents, said Columbia Law School Professor John Coffee.
Search warrant applications limit the search to the specific evidence being sought - a safeguard aimed at preventing investigators from conducting overly broad searches.
Search warrants are not an indication that someone is guilty.
FBI agents seeking search warrants involving high level officials often will consult with federal prosecutors before proceeding.
"For someone like the former president, it is highly likely that investigators would review a search warrant application at the highest levels of the Department of Justice," said Stephen Saltzburg, a law professor at George Washington University and a former U.S. deputy assistant attorney general.
Search warrants are secret until federal investigators execute them. And they can't be challenged by the person whose home, business or other location is searched.
"It can be a complete surprise," Saltzburg said. "It usually is."
After the warrant has been executed, investigators must file a document with the court that lists each piece of evidence that was seized. They must also leave an inventory of the seizures at the location where the search was conducted.
Search warrants may be challenged in court afterward if there is evidence that investigators failed to meet the probable cause requirement or otherwise misled the judge who approved the warrant.
In a federal indictment unsealed earlier this month, federal prosecutors charged members of the Louisville Metro Police Department with falsifying the affidavit they filed to obtain a search warrant for the home of Breonna Taylor, who was shot and killed by officers who executed the warrant.
Such allegations of law enforcement misconduct "are very rare, but they do happen," said Saltzburg.
What's a subpoena?
Federal law enforcement officials issue subpoenas - legal demands for evidence - when there's less potential that the material might be destroyed or hidden.
Unlike search warrants, the person who's served with a subpoena may file a court motion to quash the demand on grounds that it's overly intrusive or burdensome to provide the information being sought.
There's no public indication that Trump was subpoenaed for the material FBI agents seized during Monday's search. Andrew Weissmann, a NYU Law School professor and a former lead prosecutor in Robert S. Mueller's Special Counsel's Office, said U.S. Attorney General Merrick Garland likely asked FBI investigators why a search warrant and not a subpoena was necessary for the material sought from Trump.
"He must have gotten a really compelling answer that there was a danger the material would not be provided in response to a subpoena," said Weissmann.
Attorneys representing Trump have filed court challenges to numerous subpoenas. Among them were legal demands for Trump financial and business records by a congressional committee and the New York Attorney General's Office.
A New York court ordered Trump to pay a contempt fine after he failed to comply with the attorney general's subpoena. The court subsequently lifted the contempt finding.
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How do federal grand juries work?
The Fifth Amendment of the U.S Constitution provides that no one "shall be held to answer for a capital or otherwise infamous crime" without a presentment or indictment voted by a grand jury.
If federal investigators gather sufficient evidence to proceed in court with a criminal case against Trump, the former president would likely be charged in a federal grand jury indictment. There has been no public sign that such a case is imminent.
Potential grand jurors are summoned to court to serve on panels for varying time periods. A grand jury consists of 23 people, and votes of twelve members are required to charge someone with a federal crime.
Grand juries have authority to issue subpoenas that require testimony by specific witnesses. Successful challenges of such grand jury subpoenas are rare, said Saltzburg.
Prosecutors typically question witnesses who appear before grand juries. Grand jurors themselves may also take part in the questioning.
Grand jury proceedings are secret. But witnesses who testify before the panels are not barred from discussing their testimony.
"Grand juries can gather a lot of information before anyone knows about the proceeding," said Saltzburg. "It's an enormously powerful investigative tool."
This article originally appeared on USA TODAY: FBI search of Trump Mar-a-Lago home raises questions. We have answers.