Chilling details have emerged of 13-year-old Jayme Closs’ kidnap ordeal as the man charged with her abduction admits he chose her at random after watching her board a school bus.

Prosecutors described in court papers released Tuesday morning (Australian time) a brutal ordeal in which Jake Patterson, 21, shot Jayme’s father and then killed her mother after ordering her to duct-tape the teen’s mouth shut.

The harrowing account came just days after Jayme 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.

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

The home where teenager Jayme Closs lived with her parents in Barron, Wisconsin.

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 Jayme’s parents, Patterson taped her ankles, locked her in the boot of his car trunk and drove her to his home, passing police cars with their sirens on responding to the shooting, he told police.

Jayme managed to flee when Patterson was not at home and was found by a woman walking her dog last week.

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

Looking frail, dishevelled with matted hair and wearing shoes too big for her, Jayme spotted Jeanne Nutter and yelled out: “Please help me! I don’t know where I am! I’m lost!”

Ms Nutter recognised Jayme immediately due to the enormous public campaign to find her after she disappeared from her home town of Gordon, some 120 kilometres away, on October 15 after her parents James and Denise were shot dead and the front door was left open.

While Jayme 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.

-with AAP