A strange motive has emerged for the confessed arsonist suspected of setting luxury vehicles ablaze in the huge Kings Plaza Mall parking garage fire on Monday morning: According to a criminal complaint, he said he believed couples were using the cars for secret sex, so he set them on fire.

On Tuesday, police say 23-year-old Evon Stephens admitted to starting the fire, telling authorities "that he was motivated ... by his belief that others used the parked vehicles for sexual activity." According to the criminal complaint, Stephens—who is reportedly homeless—also stated that he "routinely went to the Parking Garage and accessed vehicles owned by the car dealerships" that stored their stock there, and that he picked one of these on purpose.

(Courtesy of the NYPD)

The complaint notes that security cameras captured guards confronting Stephens after seeing him in the lot between 8:10 a.m. and 8:25 a.m. on Monday, before the area had opened to the public. He reportedly ignored them, heading instead for the part of the garage where a local Mercedes Benz dealer kept some of its cars.

Security camera video shows Stephens getting inside one of these models and moving around. Afterwards, that car can reportedly be seen smoking, with fire spreading throughout the structure in just a few minutes. Footage also features Stephens fleeing the scene, making an "obscene hand gesture" for the cameras as he goes, according to the complaint.

After police arrested Stephens Monday evening, he apologized for the inferno, which flared into a seven-alarm fire that required hundreds of firefighters to extinguish. Over 130 cars went up in flames as witnesses outside heard "loud explosions like bombs going off" and watched an ominous plume of smoke unfurl from the garage. All told, six civilians and 22 firefighters sustained injuries from the blaze, none of them life-threatening.

As it turns out, the vehicles qualify as interstate property, making the case a matter for federal investigators, who said Stephens signed a confession on Tuesday.