William Koch, the billionaire energy tycoon and prominent Republican donor, allegedly kidnapped and interrogated at a remote Aspen ranch a former top-level executive whom he suspected of subversion.

According to Courthouse News Service, Kirby Martensen, a former executive of several Koch subsidiaries, has filed suit in federal court seeking punitive damages for the alleged incident. The Huffington Post on Saturday confirmed the story with Martensen’s lawyer.

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In the suit, Martensen charges that in March, Koch lured him and other employees to a secluded Aspen ranch—one with no cell phone reception or connection to the outside world—under “false pretenses.” Though Martensen thought he had been called to Aspen to discuss business, he was instead interrogated, searched and held against his will for over twenty-four hours before finally being freed.

Koch’s motive, according to Martensen, was an anonymous letter Koch received in 2011 that claimed he and others were engaged in a scheme to steal from and defraud from Koch enterprises. According to the court filing, Koch ordered a secret investigation into the matter that turned up private correspondance from Martensen questioning the legality of Koch’s business practices. The days-long affair in Aspen, Martensen claims, was therefore an attempt to intimidate him into silence, and to ultimately fire him.

Martensen claims that Koch told him he was going to be subject to a routine peer review while at the ranch, but that he was instead led into a small room and harshly questioned by two Koch employees. Later that night, Martensen says he was moved to a small cabin on the premises guarded by a sheriff, whom, he was told, would prevent him from fleeing.

Hours later, and after having had his belongings searched, Martensen says Koch then refused to let him catch his scheduled flight out of Aspen. Instead, he was forced into an SUV and driven to Denver where he was placed on a private jet that finally released him in Oakland, California.

Oxbow, a Koch company, told the Huffington Post that Martensen was in fact investigated, but only because they discovered he’d been defrauding the company. Martensen’s lawyer told the website that the case would probably go to trial next year.