A British model was kidnapped in Milan and detained for six days as her captor tried to auction her off online, Italian police have said.
The 20-year-old woman was attacked on July 11 by two men as she attended an arranged photo shoot.
She is believed to have been drugged and transported in a bag to Borgial, an isolated village near Turin, before being released on July 17.
A Polish man, who lives in Britain, was arrested on July 18 on suspicion of kidnap and extortion, state police said.
Officials have released a mugshot of the suspect, named as 30-year-old Lukasz Pawel Herba.
It is alleged two men tried to sell the woman online for more than 300,000 dollars (£230,000) and demanded the model's agent pay to secure her safe release.
The woman was kept handcuffed to furniture but was freed after six days and taken to the British consulate in Milan, despite the ransom not being paid.
It has been reported that the captor demanded £50,000 upon the woman's release and threatened to kill her if she told police about the incident.
Milan police officer Lorenzo Bucossi told reporters the group the suspect was allegedly working for offered "mercenary services" on the dark web.
According to a translation on Sky News, Mr Bucossi said: "Certainly the author of this very serious crime is a dangerous person - don't forget he was also ready to carry out a 'final solution', as he called it.
"He was a killer and was working for an organisation on the deep web that is offering mercenary services such as bombing attacks, kidnapping and the selling of girls on the dark web."
Italian police said they are working with officials in Britain and Poland as they continue to investigate.
A spokeswoman for the Foreign Office said: "We have been providing consular support to a British woman in Italy and are in touch with local authorities."