This is a promotional booklet released in Japan in order to advertise the original PSX release of The Silver Case.
I was unaware of its existence until it was scanned and archived by this VK page. As an inept westerner I am completely flabbergasted when it comes to using VK, so I hope my linking to the page is enough to put credit where credit is due.
Here’s a PDF copy of the same booklet, though I am not sure if it comes from the same source or not.
To coincide with the release of the HD version of The Silver Case, distributor Playism took the time to translate the booklets included in the original PSX release. While the boxed PC copy came with these two booklets included, they were also released digitally for free on the game’s store page.
Not many people are aware of them, so I’m mirroring them here.
The playing manual includes a useful character relations chart, which also happens to contain the first appearence of both Sundance Shot and Daizaburo Kai (who would later go on to appear in Flower, Sun and Rain), with another mysterious character, the Mulholland President Marionette Mother, who has never showed up in any of the games. From her title, however, it might be inferred that she was a key player in the Shelter Children Policy (the entrance to the underground Shelters, is situated behind the Mulholland tobacco shop).
Marionette Mother would go unmentioned for the next 22 years, until THIS Reddit AMA (Archive link), in which Suda confirmed she was originally meant to make her debut in Killer7.
It also happens to include the first mention of Death-filing, which would later be expanded in the 25th Ward and which Suda would explain in his Q&A on the original TSC website.
The Booklet originally detailed all the puzzle solutions for the actual game. The HD version actually has a button to auto-solve all the puzzles, making it superfluous. It also includes some commentary from Hiroyuki Nakata (Editor-in-Chief of GameWatch!) and an explanation of the titular Silver Case.