BEIJING — In the unpolished video that appeared on state television one October morning in 2015, Wang Yu, one of China’s most prominent lawyers, denounces her own son.

While she was herself under arrest, the young man had been detained after leaving the country without permission or the proper papers. He first flew to the southern province of Yunnan and then rode on the back of a motorcycle into Myanmar, his movements captured on closed circuit cameras.

“I strongly condemn this type of behavior,” Ms. Wang says in a monotone, sitting inside a featureless room. “This kind of action is very risky and is illegal.”

It was all a lie, as her colleagues suspected when the video first aired.

Ms. Wang’s videotaped contrition was merely an example of how the Chinese authorities routinely coerce detainees into making statements that serve the government’s propaganda needs.