The Washington State History Museum will be opening a special exhibit in August on famous skyjacker D.B. Cooper, who parachuted out of a commercial airliner somewhere between Portland and Seattle with $200,000 in extorted cash in 1971 and was never caught.

The case remains the only unsolved air piracy in American aviation history.

Museum spokesman Margo Helgen said the museum in Tacoma wanted to emphasize the exhibit is not being held to promote a criminal, but to show “the nature of personal safety” and how “hijacking has changed over time and the response to it.”...