[16][7]: 160  Cooper then made additional demands: upon landing at Sea-Tac, fuel trucks were to meet the plane and all passengers were to remain seated while Mucklow brought the money aboard.

[18] For approximately two hours, Flight 305 circled Puget Sound to give the SPD and the FBI sufficient time to assemble Cooper's ransom money and parachutes, and to mobilize emergency personnel.

"[32][33] He then gave the cockpit crew his flight plan and directives: a southeast course toward Mexico City at the minimum airspeed possible without stalling the aircraft—approximately 100 knots (185 km/h; 115 mph)—at a maximum 10,000-foot (3,000 m) altitude.

[55] On December 6, 1971, 12 days after the incident, FBI Director J. Edgar Hoover approved the use of an Air Force SR-71 Blackbird to retrace and photograph Flight 305's flightpath,[56] and attempt to locate the items Cooper carried during his jump.

[63] Using fixed-wing aircraft and helicopters from the Oregon Army National Guard, the FBI coordinated an aerial search along the entire flight path (known as Victor 23 in U.S. aviation terminology,[64] and as "Vector 23" in most Cooper literature)[46][65] from Seattle to Reno.

[68] Two local women stumbled upon a skeleton in an abandoned structure in Clark County; it was later identified as the remains of Barbara Ann Derry, a teenaged girl who had been abducted and murdered several weeks before.

[70] Based on early computer projections produced for the FBI, Cooper's drop zone was first estimated to be between Ariel dam to the north and the town of Battle Ground, Washington, to the south.

[75]: 124 [75]: 69 A month after the hijacking, the FBI distributed lists of the ransom serial numbers to financial institutions, casinos, racetracks, businesses with routine transactions involving large amounts of cash, and to law-enforcement agencies around the world.

[76] Two men used counterfeit $20 bills printed with Cooper serial numbers to swindle $30,000 from a Newsweek reporter named Karl Fleming in exchange for an interview with a man they falsely claimed was the hijacker.

"[84] The Washougal Valley and the surrounding areas have been repeatedly searched but no discoveries traceable to the hijacking have been reported,[81] and the FBI believes any remaining physical clues were probably destroyed in the 1980 eruption of Mount St.

Known as the Cooper Research Team (CRT),[95] the group included paleontologist Tom Kaye from the Burke Museum of Natural History and Culture in Seattle, scientific illustrator Carol Abraczinskas, computer scientist Sean Christo, and metallurgist Alan Stone.

[2]: 210 Flight attendants Schaffner and Mucklow, who spent the most time interacting with Cooper, were interviewed on the same night in separate cities and gave nearly identical descriptions: a man in his mid-40s, approximately 5 feet 10 inches (1.78 m) tall and 170 to 180 pounds (77 to 82 kg), with olive-toned skin, brown eyes, short combed-back black hair, and no discernible accent.

According to retired FBI chief investigator Ralph Himmelsbach, extortionists and other criminals who steal large amounts of money nearly always do so because they need it urgently; otherwise, the crime is not worth the considerable risk.

[94] Because the Dan Cooper comics were neither translated to English nor imported to the United States, FBI profilers speculated the hijacker encountered them during a European tour of duty, and spoke fluent French.

Cooper chose a seat in the last row of the rear cabin for three reasons: to observe and respond to any action in front of him, to minimize the possibility of being approached or attacked by someone behind him, and to make himself less conspicuous to the rest of the passengers.

"[7]: 321 The most significant knowledge Cooper displayed was a feature both secret and unique to the 727: the aft airstair could be operated during flight, and the single activation switch in the rear of the cabin could not be overridden from the cockpit.

An aircraft cargo-loading assignment would provide him with aviation knowledge and experience: cargo loaders have basic jump training, wear emergency parachutes, and know how to dispatch items from planes in flight.

[180] Stewardess Florence Schaffner told author Geoffrey Gray that photos of Christiansen fit her memory of the hijacker's appearance more closely than those of the other suspects she had been shown, but added that she could not conclusively identify him.

[187][188] As an eight-year-old, she recalled Cooper and another uncle planning something "very mischievous", involving the use of "expensive walkie-talkies", at her grandmother's house in Sisters, Oregon, 150 miles (240 km) southeast of Portland.

[190] In August 2011, New York magazine published an alternative witness sketch, reportedly based on a description by Flight 305 eyewitness Robert Gregory, depicting horn-rimmed sunglasses, a "russet"-colored suit jacket with wide lapels, and marcelled hair.

According to Galen Cook, a lawyer who has collected information related to Gossett for years, he once showed his sons a key to a Vancouver, British Columbia, safe deposit box which, he claimed, contained the long-missing ransom money.

"[200] Joe Lakich (1921–2017) was a retired U.S. Army Major and Korean War veteran whose daughter Susan Giffe was killed less than two months before the hijacking, as a consequence of a botched hostage negotiation conducted by the FBI.

[206] He came to the attention of the Cooper task force due to the timing of his disappearance, multiple matches to the hijacker's description, and the reasoning that "a fugitive accused of mass murder has nothing to lose".

He served prison time in 1994 for negligent homicide after two of his students died when their parachutes failed to open[209] and was later found indirectly responsible for thirteen additional skydiving deaths due to faulty equipment and training.

[215] He boarded United Airlines' Flight 855 (a Boeing 727 with aft stairs) in Denver, Colorado, and, brandishing what later proved to be a paperweight resembling a hand grenade and an unloaded pistol, he demanded four parachutes and $500,000.

[76] After delivery of the money and parachutes at San Francisco International Airport, McCoy ordered the aircraft back into the sky and bailed out over Provo, Utah, leaving behind his handwritten hijacking instructions and his fingerprints on a magazine he had been reading.

[239] In January 2018, Tom and Dawna Colbert reported that they had obtained a confession letter originally written in December 1971 containing codes that matched three units Rackstraw was a part of while in the Army.

[276] There were no further notable Cooper imitators until July 11, 1980, when Glenn K. Tripp seized Northwest Orient Flight 608 at Seattle-Tacoma Airport, demanding $600,000 ($100,000 by an independent account),[unreliable source?

[279] Due to multiple "copycat" hijackings in 1972, the FAA required that the exterior of all Boeing 727 aircraft be fitted with a spring-loaded device, later dubbed the "Cooper vane", that prevents lowering of the aft airstair during flight.

[287] Himmelsbach famously termed Cooper a "rotten sleazy crook",[288] but his bold and unusual crime inspired a cult following that was expressed in song, movies, and literature.