要逮捕一个人，警方必须先合理地判定他确实犯了罪。

To arrest a person, the police have to be reasonably sure that a crime has been committed.

youdao

刑罚必须总是量罪而定。

The punishment must always fit the crime.

《柯林斯英汉双解大词典》

控方必须毫无疑义地证明他犯有谋杀罪。

The prosecution has to prove beyond reasonable doubt that he is guilty of murder.

《牛津词典》