A public humiliation effort should be mounted to have the Good Chief removed from his position.
No, no, no! A thousand times no!
Hammer away at him to provide evidence to back up his claims, and then hammer him continually for not providing the documentation.
"I'm not calling you a liar, Chief, but you keep saying gun owners are a threat to themselves and others without ever showing the proof you have been repeatedly requested to provide."
"Chief, what evidence do you have to support your claim that gun owners are a threat to themselves and others?"
"Chief, can you explain your claim that gun owners are a threat to themselves and others when it is documented that police have more negligent discharges and shoot "innocent bystanders" than lawful gun owners?"
D not force him out of office - make him quit in the face of being shown to be both untruthful and a bigot. Or at least have his superiors terminate him for embarrassing the institution.
stay safe.