Where does “警察犬” come from?

警察犬 (Japanese) comes from Japanese 犬, from Old Japanese いぬ.

警察犬 (Japanese): police dog

Definitions

Step	Language	Word	Meaning
1	Japanese	犬	dog; canine; one who is loyal; a spy
2	Old Japanese	いぬ	—

警察犬 — Etymology, Origin & Word History | Etymology Explorer