LONGVIEW, Wash. -- The Washington State History Museum in Tacoma plans to open an exhibit in August of next year on the D.B. Cooper skyjacking mystery.

A man identifying himself as Dan Cooper hijacked a Portland to Seattle flight in November 1971. He picked up $200,000 in ransom money in Seattle and took off for Mexico, then parachuted somewhere over southwest Washington. The skyjacking remains unsolved, but some of the marked $20 bills he was given were found in 1980 along the Columbia River.

The exhibit will include some of the money. It also will illustrate features of an old Boeing 727 that have been changed in modern planes to prevent skyjackings.

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  • FILE -- The crew of a Northwest Airlines jet, hijacked Nov. 24, 1971, is seen in this Nov. 25, 1971 file photo as they appear at a news conferences at the Reno International Airport, about two and one-half hours after the jet landed in Reno. From left are Capt. William Scott, First Officer Robert Rataczak, stewardess Tina Mucklow and Second Officer Harold Anderson. The psy hear has been rich for students of D.B. Cooper, the mysterious skyjacker who vanished out the back of the Boeing 727 wearing a business suit, a parachute and a pack with $200,000 in ransom money 40 years ago Thursday, Nov. 24, 2011. (AP Photo, File)

  • In this undated file photo, a helicopter takes off from search headquarters to scour the area where hijacker Dan Cooper might have parachuted into in Woodland, Wash. The past has been a rich year for students of D.B. Cooper, the mysterious skyjacker who vanished out the back of a Boeing 727 wearing a business suit, a parachute and a pack with $200,000 in ransom money 40 years ago, Thursday, Nov. 24, 2011. (AP Photo, File)

  • FILE -- A hijacked Northwest Airlines jetliner is seen in this Nov. 25, 1971 file photo as it sits on a runway for refueling at Seattle-Tacoma International Airport, Nov. 25, 1971, Seattle. 2011 has been a rich year for students of D.B. Cooper, the mysterious skyjacker who vanished out the back of the Boeing 727 wearing a business suit, a parachute and a pack with $200,000 in ransom money 40 years ago Thursday. (AP Photo, File)

  • FILE -- This undated artist's sketch provided by the Federal Bureau of Investigation shows a rendering of the skyjacker known as 'Dan Cooper' and 'D.B. Cooper', from the recollections of passengers and crew of a Northwest Orient Airlines jet he hijacked between Portland and Seattle, Nov. 24, 1971, Thanksgiving eve. This past year has been for students of D.B. Cooper, the mysterious skyjacker who vanished out the back of a Boeing 727 wearing a business suit, a parachute and a pack with $200,000 in ransom money 40 years ago,Thursday, Nov. 24, 2011. (AP Photo/FBI, File)

  • FILE -- FBI agents scour the sand of a beach on the Columbia River in this Feb. 13, 1980 file photo, searching for additional money or clues in the D.B. Cooper skyjacking case, in Vancouver, Wash. Several thousand dollars of the hijacking money was found in the area days earlier. 2011 has been a rich year for students of D.B. Cooper, the mysterious skyjacker who vanished out the back of a Boeing 727 wearing a business suit, a parachute and a pack with $200,000 in ransom money 40 years ago Thursday, Nov. 24, 2011. (AP Photo/Reid Blackburn, File)