The movie begins in the year 1995 where there were 5 peculiar murder cases. The murderer would always get someone close to the victim to witness how he would strangle the victim from behind with a rope but he would let the witnesses go and speak to the media on how the murders happened. Ito plays the role of Makimura, the police detective who was in charge of investigating the serial murders but failed to catch the cunning murderer and his respected superior ended up being killed as well. 22 years later in 2017 when the case is nearing its statute of limitations, a man named Sonezaki claims to be the culprit for the 1995 murders and even publishes a book titled "Watashi ga satsujinhan desu" to talk about the cases. Despite the disgust towards Sonezaki's actions, the intensive attention showered on him via the media and SNS makes him become the talk of town.
Towards the beginning of the movie (20min or so in) the main guy starts typing in his memoir. He starts having flashbacks and during those they show a dead dog and a severely injured cat and dog. He is a veterinarian. The dead dog he had to dissect to get a wedding ring out. It made him so mad that the woman made him do that so he kills her. He doesn't like hurting animals. He ends up accidently giving a cat too much medicine due to his dementia and the cat ends up dying. This scene with the animals is very graphic and upsetting. They do show the dissection and the dog he holds looks very realistically dead.