Not to be alarmist, but with police troubles in the USA and the rest of the troubles around the world, this might be a good time to note that although the noun "the police" is always plural in English, the noun die Polizei is dealt with quite differently in German.

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Die Polizei ermittelt wegen Hausfriedensbruch.

The police are investigating because of [criminal] trespassing.

Caption 12, Atomkraft - Streit um AKW-Laufzeiten

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Ruh dich aus, bis die Polizei kommt.

Relax until the police come.

Caption 15, Die Pfefferkörner - Eigentor

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Die Polizei sprach von hunderttausend Menschen.

The police spoke of one hundred thousand people.

Caption 4, Papst Benedikt - Erster Rücktritt eines Papstes in der Neuzeit

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In English, there is no singular for the noun "the police", but in the German die Polizei, there is no plural noun form. As you can see in the above examples: die Polizei ermittelt, die Polizei kommt, and die Polizei sprach, the conjugations of the verbs used reflect a singular noun.

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Further Learning
Do a search for the noun Polizei on Yabla German and see the many examples of how this word is used in German in a real world context!