News of Alibaba cofounder Jack Ma’s disappearance from public view has driven heated speculation across social media in recent days. The whereabouts of the billionaire entrepreneur are unknown and Alibaba isn’t commenting.

Formerly China’s richest person, Ma’s last public sighting was at Shanghai’s Bund Summit in late October, where he criticized Chinese regulators for stifling innovation. By early November, he was reportedly summoned to a meeting with Chinese authorities, who then pulled the plug on the planned IPO of his fintech giant, Ant Group, on November 3, just two days before it was slated to begin trading. Alibaba is now under investigation for monopolistic behavior, according to a statement from the government’s market supervision arm. And the billionaire has not been spotted since late October. Alibaba and Ant Group did not respond to Forbes’ request for comment. In a report on Tuesday, citing a person familiar with the matter, CNBC reported that Ma was not missing, just laying “The big picture seems to be that [Ma] got too big for his britches, both in independent speech as well as in actual financial power,” says Andrew Nathan, a Columbia University professor who focuses on Chinese politics. “So whether he was detained or voluntarily laying low, either one is a version of the Party reasserting its absolute power.”

Ma’s absence from the public sphere is part of a larger pattern. As Forbes has reported before, in recent years at least half a dozen other billionaires and wealthy businessmen have vanished from public life for a period of time after running afoul of the Chinese Communist Party. In December 2015, reports emerged that Guo Guangchang, founder and chairman of investment conglomerate Fosun International, had gone missing. Social media posts claimed that witnesses saw Guo being taken away by the police at Shanghai’s airport.