For 27 years, Knight avoided making a campfire for fear of drawing attention to himself. He stole what he needed to survive from campgrounds; in fact, everything he had was stolen except his eyeglasses. If there's not much reason to be found, as in Knight's case, costly police investigations are unlikely. But, eventually, Knight's thefts of food and survival supplies prompted local law enforcement to get involved.
It would take a possible federal criminal violation in addition to a disappearance, such as a fugitive or kidnapping situation, for the FBI to become involved, said FBI special agent Kathy Wright.
"The FBI requires an authorized law enforcement purpose to conduct an investigation," she said. "The mere fact that an adult disappears, is not, on its own, a violation of law."
In the end, a surveillance camera set up specifically to catch Knight triggered an alarm when he entered a campground kitchen looking for food, and Knight was arrested.
While technology -- such as thermal imaging that detects people by tracking body heat -- is helpful in pinpointing a location once a general area is mapped out, investigators haven't abandoned old-fashioned methods. In the case of Troy James Knapp, also known as The Mountain Man in Utah, it was snowshoe tracks that eventually gave him away.