Norwegian police have found the belongings of Julian Assange’s associate, cyber security expert Arjen Kamphuis, who mysteriously went missing in late August.

The 47-year-old co-author of a handbook for investigative journalists on how to keep themselves and their work safe from government spying, has been missing since August 20. At that time, Kamphuis checked out of a hotel in the town of Bodo in northern Norway and hasn’t been seen since.

.@JulianAssange associate and author of "Information Security for Journalists" @ArjenKamphuis has disappeared according to friends (@ncilla) and colleagues. Last seen in Bodø, #Norway, 11 days ago on August 20. pic.twitter.com/dV75NGKpgI — WikiLeaks (@wikileaks) August 31, 2018

The security expert’s belongings were found on Tuesday by a man who was fishing near Bodo, police said on Wednesday, as cited by Norwegian media.

According to police inspector Bjarte Walla, the fisherman “found an object floating in the sea.”

“We can say that this item belongs to missing Arjen Kamphuis,” he said, refusing to release any information on the nature of the item or items found.

Earlier in September, Norwegian police confirmed that they had detected a signal from a Kamphuis' phone near Stavanger, some 1,000km (620 miles) from Bodo.

Police say they are working on at least three theories about Kamphuis’ disappearance. Investigators say that he might have been involved in some incident, been the victim of a criminal act, or just went into hiding.

The disappearance of the Assange's associate cyber security expert also created multiple theories on Twitter, ranging from a hiking incident to a secret assignment. Some Wikileaks supporters even suggested he might have been snatched or killed in a covert CIA operation.

Captured or killed by agents of the five eyes alliance? — Bjornar Simonsen (@BjornarF1) September 2, 2018

Could He Be On A "Classified" Or "Undercover Assignment" ? pic.twitter.com/RY1uljuh8x — System_On_Chip (@US_Officials) September 2, 2018

I suspect #CIA dirty tricks — Van Tomas (@VanTomas2) September 2, 2018

Human rights campaigner Peter Tatchell believes that Kamphuis’ disappearance is certainly a “cause for concern,” because his research has been been “a matter of some considerable anxiety to government security agencies.”

“Quite clearly there are people in governments and security services around the world who would very much like to get the solution to that encryption and those cyber security measures that he's enabled journalists to use when those journalists are investigating, exposing bad things being done by governments,” Tatchell told RT.

Kamphuis has been training journalists, human rights workers and whistleblowers to defend their data from government intrusions or manipulation since 2009.

In the handbook, which he co-authored, Kamphuis advises investigative journalists and media professionals how to avoid being snooped on by the state. "Think of ‘protecting your system’ as building a house of cards – for it to work, you must build your security from the bottom up,” the handbook states.

In 2017 the security expert was interviewed by RT about the WannaCry ransomware attack. Back then he suggested that Microsoft could have left the vulnerability open on purpose at the request of the US intelligence agencies. “It could be that this particular tool for that type of crime is just slightly more effective than many of the other ones... It is using some of the vulnerabilities that were purposely built into Windows systems at the instructions of the NSA,” Kamphuis told RT.

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