This is the 15125th most frequent Russian word.
полицейскому
"Полицейскому" means "to the policeman" in English.
Dative case is used here, indicating the indirect object receiving the action.
Я передал документы полицейскому.
I handed the documents to the policeman.
Dative case is used again to show who is being trusted in the context of the verb 'доверять'.
Мы доверяем полицейскому в этом деле.
We trust the policeman in this matter.
The dative case is used to indicate the recipient of the necessity inferred by the action described.