Aubrey Sacco's father has returned from Nepal after searching for his daughter, who has been missing since April, apparently after embarking on a 10-day trek into the Langtang valley north of Kathmandu. Though Paul Sacco concedes his 23-year-old daughter, a University of Colorado-Boulder grad who grew up in Greeley, might have fallen into harm's way, he remains optimistic that she may re-appear. "I'm telling you, this girl is one tough chick," he tells the Daily Camera, less than one week after returning from the month-long search. "She's very different; she's not like anyone else." There's no evidence his daughter has been murdered, Sacco says. And now, FBI agents are looking into the disappearance, treating it as a missing-person investigation, according to The Greeley Tribune. But the FBI may be limited in what it can do. "As far as being on the ground out there," Paul Sacco says, "they will probably still have to rely on the Nepal people."