Authorities are unsure if she has a connection with the attack, but say she is important in establishing and clarifying Paddock's timeline leading up to the mass shooting.
Paddock's live-in girlfriend, Marilou Danley, was in the Philippines at the time of the attack, where her family said she was "sent away" to so that she wouldn't interfere with Paddock's plans.
Danley spoke with the FBI upon her return to the United States on Wednesday and said that she was concerned for Paddock's "mental stability."
In a statement made through her lawyer after she spoke with authorities, Danley said that she had no knowledge of Paddock's plans.
Investigators search for clues as to why Paddock, who was found dead of a self-inflicted gunshot wound, carried out the deadliest mass shooting in modern American history. A mysterious piece of paper was found in the Mandalay Bay hotel room Paddock used to open fire from on the Route 91 Harvest Festival, but officials say it is not a suicide note. In fact, investigators say there is evidence supporting the theory that Paddock originally planned to escape the hotel alive.
Paddock killed 58 innocent concertgoers on Sunday night, as well as injuring hundreds more.