Perhaps, but there's the challenge of who gets to declare genocide formally. A city mayor no matter how large probably shouldn't be able to unilaterally do so when no authority recognized by his nation does so.

I agree Netanyahu should be arrested, but I just don't think a city mayor can reasonably unilaterally do so. Certainly from a practical standpoint it's a nightmare if your own federal government will be at odds over the arrest of a foreign leader.