Daylenn Pua

Daylenn Pua, an 18-year-old inhabitant of Oahu, Hawaii, set out to climb the notorious Haiku stairs on January 27, 2015, a structure constructed during World War II to access the 2,800-foot-high radio station at the top. The Haiku Stairs provide some fantastic panoramic views of the surrounding landscape, despite the fact that they are not a particularly desirable hiking destination (the stairs are currently in a disused, decaying stage). Around 11:00 a.m., Pua began his hike and almost immediately began sharing live photos on his social media profiles.

Unfortunately, that was the last time his family or anybody else heard from him; Daylenn Pua has been gone ever since. The most unsettling aspect, though, was a minute element in one of the images. A man's figure was discovered during a more thorough investigation by forensic specialists hiding on the route and maybe following Pua. Although he is currently the main suspect in the investigation, his face is rarely recognisable, therefore this is hardly a lead.

• Year: 2015