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Alan Dershowitz said the FBI must play its cards right to get the most information possible from the girlfriend of the gunman responsible for murdering dozens in Las Vegas on Sunday.

Stephen Paddock allegedly encouraged Marilou Danley, 62, to leave the country in the days before he opened fire on a country music concert, leaving 59 dead and more than 500 injured. Danley, who was in the Philippines at the time of the shooting, touched down at Los Angeles International Airport on Tuesday, and was met by FBI officials.

Dershowitz said the FBI will get more information from Danley by convincing her she is not a suspect, merely a source of information about her former live-in boyfriend.

"If she begins to believe that she is a suspect, she's going to get a lawyer, the lawyers are then going to begin to play chess with the government," the Harvard law professor emeritus told "Fox & Friends."

Dershowitz recommended authorities ask Danley to remember details that may not have meant anything to her at the time but may mean something now, such as whether Paddock got calls from foreign sources.

The FBI could also warn Danley they could make a case against her, such as investigating whether $100,000 the killer wired to the Philippines was "hush money" for her, the lawyer added.

Paddock allegedly berated his girlfriend in public frequently, a Starbucks employee who saw them often said.

Danley's sisters, who live in Australia, claimed she knew nothing of her boyfriend's plans and was "really in love" with him.

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