In 1995, five mysterious murders took place. In 2017, a man named Masato Sonezaki comes public confessing that he is the murderer, but the police cannot arrest him due to a loophole in the law. Sonezaki publishes a book and becomes a celebrity. Later, another man claims to be the real murderer. But then it is revealed that both of them are frauds. Sonezaki confesses that he wanted to capture the real killer while the other man wanted financial success. Sonezaki is revealed to be Takumi Onodera, whose fiance was killed by that killer. Later, Sonezaki finds out the real killer's hideout and tries to kill him. Detective Ko Takimura comes and stops Sonezaki. The killer is then taken to police custody.

In a post-credit scene, a man attempts to kill the killer to avenge his mother.

https://en.wikipedia.org/wiki/Memoirs_of_a_Murderer_(film)
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