It's been in the movie. About a
cartoonist helped the police
department to unveil the most misterious veil of a serial killer
with the name Zodiac.
The idea came from the real story. Zodiac was alive in the year 60s to 70s in California. Had assassinated thirty seven people. In some cases, he called up the police like it was a challenge for him, he confessed that he's the killer. And also sent the letters to the cop, the cop should guess what is the meaning of the words in the letters which referring to the next target of his action crime. The victims fell when the police coldn't guess the meaning of the hint letter.
Zodiac gave a symbol to sign that it was his doing 'only'. But also probably to amplify his winning echo to scare the townsfolk. A circle, pierced by one horizontal line and one vertical line, resembled to a target sign in the shooting range. Superheroes in the movie have the marks as their identity in order to nobody can imitate them. This one too. Though not into the form of red uniform and spider web power, as Spiderman.
In the movie, the only who could unveil his identity was the persistent
cartoonist himself. In the real life, Zodiac is still out there, prowling. According to the rumours, he had gone abroad. The case was closed by San Fransisco's police
department in 2004, they opened it again in 2007.
Zodiac however was a brained man and defying everything to prove his cleverness. He felt he was so smart, even the cops can't apprehend him. So he made those letters to give a little clue, as still he was hiding by the dark. The newspaper had been forced to publish his letters, or another victim will be found died. According to the police's estimation, sometimes he wanted to show off, wanted to confess but then it was off. Unconsciously he had the need to be known by people of his doing, he seen that as a pride.
The movie length was long, to three hours. Finally they got a suspect, but without proof. After years later, the cartoonist had found something in his muse. He connected all the data in his head then rummaged the file cabinets in the police station without permission in the midnight, to match what he got in his head with the information in their files. After that, they got the real Zodiac from the released suspect and caught that guy.
Besides Zodiac, there was Jack The Ripper. Jack The Ripper story had been filmed with Johnny Depp as the main star, and the title was From Hell. The victims were the sluts, found died in the dark passages. And the detective's premises were: maybe he had a bad experience with a slut, or his mother was a slut so he was so embarrassed to see her mother's disgrace in every sluts, or had been blackmailed by a slut till he was vengeful, or he had a girlfriend dumped him and she was a prostitute. Or, the most logical 'the sluts were only trash in his eyes, and he wished with his action would subtract their number.'
Jack The Ripper stayed in England in the nineteenth century before crossed over the Atlantic Ocean, then settled down in U.S.A. The killing happened in Whitechapel, London. By cut the victim's neck and did some mutilations. The cops thought he had a medical education background. He slashed like the way a surgical doctor did, very neat slashes.