The word “police” is a plural noun. When you are using the word as a subject in your sentence, use only the plural verb with it.
The police is or are investigating
Correct: The police are investigating.
The police is or The police are coming.
Correct: The police are coming.
The police has or the police have
Correct: The police have
What is the singular of police if it is a plural noun?
The singular of police is police man.
The police man has arrested two thieves.
The policeman is coming.