It's a thriller about a psychopath who's killing people. In the end it is revealed who the killer is.
It's a movie is about a guy killing people.
It's a movie about a crazy person killing people.
kyouheiさん
ご質問どうもありがとうございます。
様々な表現があると思いますが、いくつか自然な表現を紹介します。
1. It's a thriller about a psychopath who's killing people. In the end it is revealed who the killer is.
--- psychopath = サイコパス
--- to reveal = ～を明らかにする / ～を明かす
2. It's a movie is about a guy killing people. And in the end you find out who the killer is.
3. It's a movie about a crazy person killing people.
お好みに合わせて使い分けてみてください。
ご参考にしていただければ幸いです。
It's a movie where people get killed one right after another, and they don't know who the murderer is until the very end of the movie.
この場合、次のような言い方ができますよ。
A: What's the movie about?
「それはどんな映画なの？」
B: It's a movie where people get killed one right after another, and they don't know who the murderer is until the very end of the movie.
「人々が次々と殺されて行くんだけど、映画の最後の最後まで誰が犯人かわからいっていう映画だよ」
to get killed one right after another で「次々に殺される」と言えます。
ご参考まで！
ドイツ 
カナダ 
