Norwegian police have launched an investigation into the disappearance of Arjen Kamphuis, a Dutch cybersecurity expert and WikiLeaks associate who was last seen two weeks ago in Norway.

WikiLeaks posted an updated tweet Saturday about the “strange disappearance” of a man who has described himself as a “digital self-defense professional.”

Kamphuis, 47, was last seen Aug. 20 checking out of his hotel in the Norwegian town of Bodø. He was scheduled to fly to Amsterdam two days later out of Trondheim, 450 miles south of Bodø.

“We have started an investigation,” a Norwegian police spokesman told Agence France-Presse. Police won’t “speculate about what happened to him,” he said.

Information about his disappearance was first posted on Twitter on Friday by Ancilla van de Leest, a member of the Dutch Pirate Party and a privacy activist. “Friends, colleagues and family are very, very worried,” she wrote. Van de Leest contacted police and newspapers and an extensive cyber network to get the word out about her missing friend at #ArjenKamphuis and #FindArjen.

Kamphuis’ disappearance has triggered a slew of conspiracy theories on Twitter, particularly given his connections to WikiLeaks and its founder Julian Assange, who published Democratic Party emails hacked by operatives linked to the Kremlin.

But the cybersecurity expert is also described in the missing poster as an “avid hiker,” and some speculate that he could be lost or injured in the wilds of Norway. He describes himself on Twitter as a “free software advocate, mountanieer, sailor, carpenter, geek — and damn proud of it.″

Van de Leest sent out a call on Twitter for anyone with drones, presumably to do aerial searches of outdoor areas.

Update on the strange disappearance of @ArjenKamphuis. Arjen left his hotel in Bodø on August 20. He had a ticket flying out of Trondheim on August 22. The train between the two takes ~10 hours, suggesting that he disappeared in within hours in Bodø, Trondheim or on the train. https://t.co/t4OTJZGBeT — WikiLeaks (@wikileaks) September 2, 2018

Kamphuis wrote the 2014 free handbook Information Security for Journalists to help media professionals protect their work and communications from government snooping.

Dutchman Arjen Kamphuis has dissapeared. A man with a heart for transparency.

Please help find him. #FindArjen https://t.co/94ilU2BVIt — Transparantie (@Transparantie) September 2, 2018

Privacy/free software advocate & all-round wonderful human being @ArjenKamphuis is missing. He was last seen in Bodø, Norway on Aug 20th. He’s usually dressed in black, carries a black backpack & is an avid hiker. If you have info/are in the area/have drones… FindArjen@gmail.com pic.twitter.com/qWAWjeSmk7 — Aral Balkan (@aral) August 31, 2018

The police in Bodø started their investigation this morning, They are looking for electronic traces (smartphone). Furthermore there are tips from Ålesund and other places in West-Norway. #FindArjen https://t.co/GoCvyAUsV7 — Helma (@ArtheosNL) September 2, 2018