Authorities said Helen Yunyao Zhai, Coco Yuhan Yang and John Xinlei Zhang were part of a group of teens who forced Camellia Yiran Liu to use her hands to wipe cigarette butts and ice cream from the floor of a Rowland Heights ice cream parlour.

Liu, who was 18 at the time, testified that she was then taken to a nearby park, stripped naked, kicked with high-heeled shoes, slapped and burned with cigarettes.

The three defendants, who are all now 19, were charged with torture, kidnapping and assault. Attorneys for Zhai and Yang previously acknowledged that their clients participated in the attack. A lawyer for Zhang argued in court that his client was only a bystander.

Zhai and Zhang also were charged in the beating and burning of a second teenage victim in a separate incident at a Diamond Bar strip mall three days earlier. In juvenile court, two other teenagers admitted to assault in one or both incidents, according to the Los Angeles County district attorney’s office.

Authorities believe that additional teens involved in the incidents have fled the country.

A 20-year-old man, Zheng Lu, was arrested in December on charges related to the attack.

At the preliminary hearing for the three teens, a judge said the case reminded him of Lord of the Flies, William Golding’s 1954 novel about boys who create a feral society after being stranded on a deserted island.

The teens are among thousands of young people from China who attend high schools in California without much parental supervision. In recent years, the number of “parachute kids” settling in the San Gabriel Valley has surged, mostly in Arcadia, San Marino, Rowland Heights, Temple City and Walnut.

The students typically live in private homes, paying their hosts for room, board, transportation and substitute parenting. For them, living in the US is a chance to learn a new language and culture and to escape China’s ultracompetitive college-entrance exams.

Some thrive in their new environment and go on to colleges such as the University of California, Berkeley and UC San Diego. For others, struggles with dating, friendships or school can spiral out of control without the steadying influence of parents and other family members.

In a statement read to the judge by her attorney, Yang cautioned Chinese parents against sending their children alone to the US at a young age.

“This is a wakeup call for the ‘parachute kid syndrome’,” Yang said in the statement. “Parents in China are well-meaning and send their kids thousands of miles away with no supervision and too much freedom. That is a formula for disaster.”

Zhai also told the judge that living on her own in a foreign country played a role in her actions.

“They sent me to the US for a better life and a fuller education,” Zhai said in a statement read by her attorney. “Along with that came a lot of freedom, in fact too much freedom… Here, I became lonely and lost. I didn’t tell my parents because I didn’t want them to worry about me.”

In their statements, the three defendants apologised to the victims.