The man suspected of killing Gambino mob boss Francesco “Franky Boy” Cali once tried to make a citizen’s arrest of Mayor Bill de Blasio, sources said.

Anthony Comello, 24, showed up outside City Hall a few months ago to protest the mayor and said he wanted Hizzoner behind bars, according to police sources.

The episode was just one of multiple oddball stunts the Staten Islander took part in in Manhattan, the sources said.

During his first court appearance for the killing on Monday, Comello showed off a hand covered in pen scrawls related to President Trump and the conspiracy movement QAnon.

Comello is charged with fatally shooting Cali, head of the Gambino crime family, outside the kingpin’s Staten Island home last Wednesday night.

Investigators suspect the slaying was tied to Cali barring his niece from dating Comello, law enforcement sources have said.