Should "The police is in Bangor." not also be accepted?
As far as I know, using a singular verb after a grammatical singular subject such as "the police" is always possible (and the only possibility for some English speakers), with a plural verb corresponding to the multiple individuals making up the subject possible in addition for some speakers.
I guess technically, yes, and your explanation of why is right. But still I can't for the life of me think of an example of when we'd say "The police is in Bangor" rather "The police are in Bangor". The first one just sounds weird.