A tourist broke her neck and died while sliding on a zip-wire in the northern Thai city of Chiang Mai.
Police colonel Adun Somnuk said the 32-year-old Chinese woman was sliding down a 600-metre (2,000ft) zip-wire on Sunday when a worker failed to grab her during a manoeuvre to stop her from travelling further.
She then hit another person in front.
Adun said the staff took her to a hospital where they told doctors only that she had passed out while on the zip-wire. But a post mortem later showed the woman, who was a doctor, had suffered a broken neck.
Adun said officers sent to inspect the zip-wire operation are questioning the staff and witnesses. He said the staff could be charged with causing death by negligence.