Mr. Guo explained in a March 8 videotaped interview with Mirror Media Group, a Chinese-language news company based on Long Island, how Mr. He’s son He Jintao was the “boss” of the second-largest shareholder in Founder Securities, a company in which Mr. Guo was seeking to acquire a large stake. He Jintao concealed his role through a proxy, according to Mr. Guo.

That deal soured when Mr. Guo tried, without success, to name directors to Founder Securities’ board and became locked in a dispute with his former business partner, Li You, who was the chief executive of the brokerage’s state-owned parent, according to a report by Caixin, a Chinese news company.

Mr. Guo, using turns of phrase that wouldn’t be out of place in “The Godfather” or “The Sopranos,” said He Jintao was working against him.

“To be honest, if I could publish evidence about you, He Jintao, I promise that in 24 hours, 10 million people will take to the streets and will eat you alive,” Mr. Guo told Mirror Media.

Mr. Guo, who also goes by the name Miles Kwok, did not offer any proof of wrongdoing by the He family. But for all his bluster, there is some documentation to support his assertion that the family had a financial stake in Founder Securities.

In 2015, New York Times reporters working in Beijing, Hong Kong and the southwestern Chinese city of Chengdu mapped out the financial network of He Guoqiang’s family, examining shareholding records and verifying relationships by interviewing a member of the family. Those documents and interviews show that the family did appear to control, indirectly through a series of shell companies, a stake in Founder Securities, which has a joint venture in China with Credit Suisse, the Swiss bank.