Congratulations to armadillogal and sparkyNM1955 for the FTF!
Aboard the airliner FBI agents recovered 66 unidentified latent fingerprints, Cooper's black clip-on tie and mother of pearl tie clip, and two of the four parachutes, one of which had been opened and two shroud lines cut from its canopy. Eyewitnesses in Portland, Seattle, and Reno, and all individuals who personally interacted with Cooper were interviewed. A series of composite sketches was developed. Local police and FBI agents immediately began questioning possible suspects. One of the first was an Oregon man with a minor police record named D. B. Cooper, contacted by Portland police on the off-chance that the hijacker had used his real name, or the same alias in a previous crime. His involvement was quickly ruled out; but an inexperienced wire service reporter, rushing to meet an imminent deadline, confused the eliminated suspect's name with the pseudonym used by the hijacker. The mistake was picked up and repeated by numerous other media sources, and the moniker "D. B. Cooper" became lodged in the public's collective memory.
A precise search area was difficult to define, as even small differences in estimates of the aircraft's speed, or the environmental conditions along the flight path (which varied significantly by location and altitude), changed Cooper's projected landing point considerably. An important variable was the length of time he remained in free fall before pulling his rip cord—if indeed he succeeded in opening a parachute at all. Neither of the Air Force fighter pilots saw anything exit the airliner, either visually or on radar, nor did they see a parachute open; but at night, with extremely limited visibility and cloud cover obscuring any ground lighting below, an airborne human figure clad entirely in black clothing could easily have gone undetected. The T-33 pilots never made visual contact with the 727 at all.
Initial extrapolations placed Cooper's landing area on the southernmost outreach of Mount St. Helens, a few miles southeast of Ariel, Washington, near Lake Merwin, an artificial lake formed by a dam on the Lewis River. Search efforts focused on Clark and Cowlitz Counties, encompassing the terrain immediately south and north, respectively, of the Lewis River in southwest Washington. FBI agents and Sheriff's deputies from those counties searched large areas of the mountainous wilderness on foot and by helicopter. Door-to-door questioning and searches of local farmhouses were also carried out. Other search parties ran patrol boats along Lake Merwin and Yale Lake, the reservoir immediately to its east. No trace of Cooper, nor any of the equipment presumed to have left the aircraft with him, was found. The FBI also coordinated an aerial search, using fixed-wing aircraft and helicopters from the Oregon Army National Guard, along the entire flight path from Seattle to Reno. While numerous broken treetops and several pieces of plastic and other objects that, from the air, resembled parachute canopies were sighted and investigated, nothing relevant to the hijacking was found.
In early 1972, shortly after the spring thaw, teams of FBI agents aided by some 200 Army soldiers from Fort Lewis, along with Air Force personnel, National Guard troops, and civilian volunteers, conducted another thorough ground search of Clark and Cowlitz Counties for eighteen days in March, and then an additional eighteen days in April. Electronic Explorations Company, a marine salvage firm, used a submarine to search the 200-foot (61 m) depths of Lake Merwin. Two local women stumbled upon a skeleton in an abandoned structure in Clark County; it was later identified as the remains of a female teenager who had been abducted and murdered several weeks before. Ultimately, the search operation—arguably the most extensive, and intensive, in U.S. history—uncovered no significant material evidence related to the hijacking.
Your last clue can be found north of an abandoned shack in the middle of nowhere. Did Mr. Cooper live out the rest of his days in a similar secluded location, as some folks speculate? Discover this final cache, and reveal the location of "D.B's" legendary hide.
No muggle traffic in this area, but be wary of animal traffic and droppings. NO OFF-ROADING! Please park and walk for this one.