A gang of kidnappers planned to torture and dismember Russell Crowe after abducting the star, Los Angeles police sources say.
They were going to demand £9 million for his release and, for every hour they weren't paid, they were going to cut one of his fingers off.
Officers uncovered the plot after pulling over a vehicle in Bel Air in Los Angeles, where the actor was staying, according to US press reports. Police found notes detailing the gang's plans and surveillance equipment in the car.
A police source said: "They took the driver to police headquarters and in the vehicle discovered notes detailing the comings and goings of Crowe.
"Crowe was being watched constantly to figure out his daily patterns for a group that wanted to kidnap him. The kidnappers planned to ask for $13 million from movie studios.
"If the ransom was not paid within a certain amount of time, they would cut off one of Crowe's fingers every hour. He was going to be maimed and tortured until the ransom was paid.
"And if the ransom still wasn't paid, the kidnappers were going to kill the actor."
Detectives haven't identified the suspect. There are unconfirmed reports the group is linked to South American revolutionaries or drug dealers.