Antonius Verwey, 43, booked into the Ventures Hotel, Paddington, west London, for one night in May. He then booked a second night, but never returned.
His clothes, camera and return ferry ticket were left in the room.
Hotel staff alerted police, and investigations in Britain, Holland and Belgium convinced detectives that Mr Verwey had been poised to make a cannabis deal.
Detective Superintendent Bill Scholes, leading the inquiry, said: 'A number of criminal associates have told me they believe he is dead.'Reuse content