After it was clear that Cooper was not on board, FBI agents quickly converged upon the aircraft. Unfortunately, there wasn’t nearly any physical evidence onboard. Among what authorities acquired was: a black clip on tie, eight cigarette butts, and two of the four parachutes that Cooper had left behind. Afterwards, the FBI  conducted interviews with the flight crew concerning the appearance of Dan. He was described as a white male with brown eyes and dark hair. 

Alongside these details, he also appeared to have been in his mid-40’s and wore a dark trench coat, dark suit, white shirt, black tie, dark shoes, and he donned a pair of sunglasses shortly after he boarded the plane. The FBI quickly conducted the first of various composite sketches, attempting to match the description of Cooper given by the witnesses. Instead of attempting to immediately launch a search operation based on the sketches, the FBI instead needed to determine exactly where D.B. had dove out of the plane. Since none of the four crew members nor the two fighter jets that were escorting the flight visibly witnessed Dan leaping out from the aft stairway, the flight crew did recall something feeling odd to them. The last communication between the flight crew and Dan occurred at approximately 8:05 P.M., when the flight crew asked if they could offer him any form of assistance, of which was declined. 

Shortly thereafter, the crew described feeling and hearing an oscillation or vibration of the aircraft, which could’ve been caused by Cooper’s potential departure. Since this took care of the when, the FBI then shifted their attention to determining the where. Dan refused to file a specific flight plan due to his impatience with the pace of the refueling in Seattle, so the pilot decided to fly along an airway known as Victor 23 after the aircraft had taken off. Authorities were then able to determine that the approximate departure time was somewhere within 25 miles north of Portland, Oregon. At dawn, the FBI then launched a search operation including helicopters, boats, and ground troops. However, due to approximation being the closest unit of measurement towards D.B. Cooper’s bailout point, his exact bail point was going to be far more difficult to pinpoint.