crimeは可算名詞としても不可算名詞としても使われます。
crimeとcrimesの違いは、clothingとclothesの関係を考えると分かりやすいと思います。

私の著書でも説明したように、clothingは着物がごちゃまぜになっていてどれがどれか分からない状況の「着物、服」です。数える場合は、a piece of clothing, two items of clothingなどとします。あるいは、a sweater, trousers, two down jacketsなどと個別名を使います。

不可算用法としてのcrimeも、さまざまな犯罪がごちゃっと混ざり合っていて、ひとつひとつの犯罪を分けることができません。
可算用法では分けて考えますから、a crimeもmany crimesも可能です。特に犯罪の種類を表す場合は可算です。この点、fruitの使い分けと同じです。
Theft is a crime.
窃盗は犯罪だ。

You took my maps I had copied. It cost just a little to make those copies, but they were all mine. You knew that and took them and hid them or discarded them. Is it something a public servant should do? Theft is a crime.

To protect his own position, he forced中山女性職員に２０１８年５月１日,Just two days before the May festival starting on May the third,の件を「記憶にない」と

嘘をつかせてしまう。
渡辺男性職員

Shame on you !

You work for a semi-public non-profit organization.
You are working for the public, the farmers in your and also my city.
You are telling a lie to one of such farmers, making fun of him.

It is such a shame.
You two have to admit your crime and you have to learn how to compensate and how to apologize as adults.

Since September 26th, 2018 and since December 12th, 2018

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