His resignation is the most significant occurrence of the four federal investigations enveloping City Hall, and the move shows that the investigations could deal more damage to the Adams administration before they’re all over.

The reason authorities are investigating Caban is unclear, but the New York Times reported that the investigation has keyed in “at least in part on a nightclub security business owned by the commissioner’s twin brother, James Caban.”

CBS News reported that his twin allegedly worked as a “fixer” for restaurants and nightclubs, settling disputes between police and popular establishments around noise complaints and other violations. 

Officials raided Caban’s residence, seizing his cellphones and, later, those of his brother. Caban maintains he did nothing wrong and resigned not as an admission of guilt.

Another major federal investigation into Adams’s administration also involves brothers.

Investigators looking into a possible bribery scheme seized phones from Terence Banks, as well as his older brothers, New York City Schools Chancellor David Banks, and the deputy mayor for public safety, Philip Banks.

One of the brothers, Terence Banks, is a consultant for a company that has received contracts with agencies his brothers oversee. The inquiry is reportedly in its early stages.

The other two federal investigations involve Adams himself and a top aide.

Investigators have inquired into Adams’s fundraising, searching the home of his chief fundraiser in November as part of an inquiry into whether the campaign worked with the Turkish government to garner illegal foreign donations. A major part of the investigation is whether Adams pressured the city’s fire department to approve a Turkish high-rise and accepted airline upgrades on Turkish Airlines, which is owned in part by the Turkish government.

That case could have devastating complications for Adams.

The final case implicates Adams’s Asian affairs liaison, Winnie Greco, who has close ties with the Chinese community in New York City. It’s unknown what exactly Greco is being investigated for, but her home was raided earlier this year.

The same prosecutor’s office, the U.S. Attorney’s Office for the Eastern District of New York, has charged several people with acting improperly on behalf of China’s government in recent years.