This week’s mistake is a common one, and while native speakers might still understand you if you mix them up, it’s definitely one to avoid if you want to improve your English.
The word „police“ is always plural in English, so you should always use „are“ after it. The phrase „The police is“ is grammatically incorrect.
Here’s the correct response to a typical question below.
A: Who’s investigating the robbery?
B: The police are working on it right now.