A Wisconsin man admitted that he kidnapped a 13-year-old girl he picked out at random after seeing her board a school bus and held her hostage for three months after killing her parents in their home, prosecutors said in court papers on Monday.

Prosecutors described a brutal ordeal in which Jake Patterson, 21, said he shot Jayme Closs's father and then killed her mother after ordering her to duct-tape the teen's mouth shut.

Patterson is expected to appear in the Barron County Circuit Court on Monday to face charges including two counts of intentional homicide, one count of kidnapping and armed burglary.

The harrowing account came just days after Closs ended her 88-day captivity by escaping the rural home where, according to authorities, Patterson kept her trapped under his bed for as much as 12 hours at a time.

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"When he made her hide under his bed, he stacked totes and laundry bins around the bed with weights stacked against them so she could not move them without his being able to detect it if she did," the complaint alleges.

The criminal complaint states that the suspect "made it clear that nobody was to know she was there or bad things would happen to her."

Escape

Patterson told police he first saw Closs getting on the bus last fall and decided he wanted to take her, prosecutors said.

What followed was weeks of planning, in which Patterson stole license plates to replace his own, checked out the Closs home twice, purchased a black ski mask and shaved his head to avoid leaving any hairs at the crime scene, police said.

After killing Closs's parents, Patterson taped her ankles, locked her in his boot and drove her to his home, passing squad cars with their sirens on that were responding to the shooting, he told police.

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Closs managed to flee when Patterson was not at home and was found by a woman walking her dog on Thursday afternoon.

The two then approached a neighbour's house to call police.

While Closs warmed up inside, the neighbour, Peter Kasinskas, retrieved his gun and stood watch at the door in case her captor was searching for her, according to the Duluth News Tribune.

His wife, Kristin Kasinskas, a middle-school teacher, realised she taught Patterson as a student but did not remember him well, the newspaper reported.