Police
noun, の adjective
They warn you and they guess when you've done something wrong (with evidence, of course!). They are the police.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
動くな！警察だ。
Don't move! It's the police.
きっと警察は助けてくれません。
I am sure the police will not help me.
警察に電話した方がいいんじゃない？
Maybe we should call the police?