Imprison the mayor pending trial, in 6 months, without bail, and the city will be more forthcoming.
In New York’s case - there’s a good chance they wouldn’t miss their mayor.
As deeply satisfying as it might be to toss the good mayor into Epstein's last domicile, that is absolutely the wrong thing to do, mainly because it would then devolve into nothing but a political morass.
What ICE should be doing is to send a few agents directly to the police department. Request whatever information they need and then await the response. If the clerk, cop or whomever refuses to cooperate, arrest him/her for aiding and abetting a fugitive. I guarantee you that if you or I had 30 or so illegals stashed in our basement, the police, ICE, or whomever would be more than willing to arrest either of us for any number of things. Why should some governmental functionary be able to get away with essentially the same thing? No. Just arrest him or her, then wait for the replacement drone, and make the same request. If that person refuses, make another arrest. Eventually you will run out of people, or someone will start cooperating.
This is not rocket science. It is the law. You and I are responsible for knowing and adhering to each and every one of the hundreds of thousands of laws that smother our society. Why the hell doesn't it apply to government functionaries? Simply enforce the law until you get some cooperation.