© TwitterPolice 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 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.
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.
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
Comment: Dutch cyber security expert linked to WikiLeak's Julian Assange mysteriously disappears in Norway