非親告罪【ひしんこくざい】 vs 親告罪【しんこくざい】
To my understanding 親告罪 means: A type of crime which requires a formal complaint from the victim in order to prosecute.
非【ひ】 means: a mistake, negative, injustice, non, un, etc...
So is the first word like a double negative? In other words like not a crime? A conversation of these two words happened during a talk recently and I didn't quite fully understand. Any in-depth explanation would be great!
非親告罪 doesn't mean decriminalization. It means non-親告罪、that is to say, investigative organization can prosecute the accused without a requirement for a formal complaint from the victim in order to prosecute.
When you see the Kanji 非 used before another word, you should always suspect it is used as a prefix in order to make it opposite of the word without 非.
For example,
[常識]{じょうしき}: common sense vs 非常識: lack of common sense, or absurdity.
[紳士的]{しんしてき}: gentlemanly vs 非紳士的: ungentlemanly
[会員]{かいいん}: a member vs 非会員: a non-member
Therefore, 非親告罪 means the opposite of 親告罪, in other words, 非親告罪 is the crime that is not 親告罪 in the same way as 会員 means a member and 非会員 means someone who is not a member.
There are other suffixes that have similar functions to 非 such as 不, 未 and so on. They have different usages and have to be learned on a case by case basis.