The Game Mansion Murder Case File 3 - S1-E25
Stupidity: The killer's plan is rather clever, but there's a huge hole in it; assuming the killer needs to be part of the game to set up the traps, there's absolutely no reason for the person they want to -benefit - from the crime to be part of the game. In fact, it is absolutely crazy; they were not involved at all, ignoring who the victim was, and if you wanted them to inherit from the victim, you'd want them to be MILES away from the crime instead of endangering them and inevitably implicate them. If all went smoothly, the police and media would surely have been on their case for the huge coincidence; they survive a murder and inherit from the victim of said murder.
Inspector Kenmochi the Murderer File 4 - S1-E22
Stupidity: The finale is sweet, but also the ultimate stupidity; there was a recording of the victim completely discharging one of the suspects from any blame, the recording was in one of the key evidences found by the police and used in the trial, but nobody ever played that recording. At least two families have to sue the State for a horrible job.
Inspector Kenmochi the Murderer File 4 - S1-E22
Stupidity: The denouement in this episode does not make any sense. Two characters (the lawyer, the victim's sister) are suddenly present on the scene for the climax, but they were never invited and if they were at the hospital in the corridor right at that moment, Busujima could not sneak by Kenmochi's room. Later Kindaichi gingerly explains the rest at the other crime scene, which is in a different building somewhere else in the city - and they are all physically there, even the patients in their hospital gowns and slippers, it's not a dramatic rendition.
Inspector Kenmochi the Murderer File 2 - S1-E20
Stupidity: Kindaichi has to talk to the lawyer of the case from three years back to learn about the gruesome details of the torture on Marina. However, those would be in possession of the police as well, and he has their full cooperation. (00:11:20)
The Prison Prep School Murder Case File 5 - S1-E14
Stupidity: When the Puppeteer is shot, like any good villain he's actually wearing a bulletproof vest. However, a bulletproof vest is not a magical forcefield that neutralizes kinetic energy; this guy barely flinches when hit. Neither are flames; his fire trick raises a literal firewall, but firewalls are not literal walls, they do not stop bullets. The policemen could easily keep shooting through it (he throws a glove at Kindaichi through it), but they just do not, for no reason.
The Prison Prep School Murder Case File 3 - S1-E12
Stupidity: When Kirisawa's body is discovered, it means that he was completely overlooked during the headcount and at every point during the day. With students disappearing left and right, that's a pretty big oversight - that somehow the killer anticipated, because his body discovered last was crucial for the plan.
The Prison Prep School Murder Case File 2 - S1-E11
Stupidity: The whole story of the 5 episode arc requires unhealthy amounts of suspension of disbelief; the killer directly challenged the police and announced where and when the murders will take place; at a 3 days prep school camp. Despite that, one of the teachers, a new one at the job even, is allowed to attend the camp wearing a ski mask, supposedly to hide hideous burns, and the police just lets him in without checking. And yes, he's the criminal, not even a red herring. By comparison, in the live version adaptation they check him, and he's wearing prosthetic scars.
The Prison Prep School Murder Case File 1 - S1-E10
Stupidity: Paragon of cleverness inspector Adechi somehow did not check for any trap in the mysterious box he received, and brought it to a crowded cafe just, so he could show it to the kids. For the explosive trick to work, the puppeteer needed also to know exactly where Kenmochi would be seated and which seats would later Kindaichi and Miyuki pick, since the box had to be at such an angle that the puppet would be propelled to the exact spot on the roof that acted as podium.
The Alchemy Murder Case File 4 - S1-E9
Stupidity: Everyone mentions in the first episode that the various doors are made out of different metals (some rather unlikely; a door made out of pure manganese?) but they don't show it, all have the same color and weight (the door made out of lead and the one made of tin would be significantly different, and one is the treasure, 966 kg). More importantly, since it's a known fact that the doors are made out of different metals, each has a number that matches the periodic table, and they are looking for gold, the supposedly hard enigma concocted by the genius alchemist is something a high schooler would figure out in minutes; Miyuki even knows its atomic number by memory when randomly asked.
The Hong Kong Kowloon Treasure Murder Case File 1 - S1-E1
Stupidity: Saki is a high-schooler visiting Hong Kong with his parents, but at no point do they communicate; the plot unfolds for days without the slightest mention of them, mentioned again in one throwaway line in the last episode. He even has to sleep on the floor cooped up at the bellboy's house with Kindaichi.
The Prison Prep School Murder Case File 5 - S1-E14
Stupidity: The plot could work only if everyone part of the trip were completely silent during the day; even walking through the empty corridors to go from one class to the next at the top of the hour would have inevitably tipped the other group that there was someone else nearby. Some even scream or freak out hitting things.
The Prison Prep School Murder Case File 2 - S1-E11
Stupidity: Akechi finds the pieces of chalk but does not investigate the open locker, where the victim left what turns out to be literally the name of the murderer. The plan of the all-knowing Puppeteer works only because the smart investigator does not perform even the most basic crime scene.
The Alchemy Murder Case File 3 - S1-E8
Stupidity: The plot throws in a drawing from a XVII century tome asserting that the building was designed with alchemic purposes by the scientist who built it. Wonderful, but the concept is not carried out coherently; the elements (as in, elements from the periodic table, which does not fit the era already, but let's say it was an original take) are placed with no relation to the basic scheme. For instance, Tin is in the "Moon" position, and its murder was executed with Fire, and some intersections have one room, some two, with no logic.
The Alchemy Murder Case File 1 - S1-E6
Stupidity: Kindaichi is on the set of a reality show, with a film crew. When one person goes missing, he is the one who comes up with the idea to tell those people, a reality show film crew, to check the footage of the cameras, and the TV people are shocked by this brilliant idea.
Reika Hayami and the Uninvited Guest - S1-E5
Stupidity: The plot hinges on the fact that the culprit switched clothes with the guy in the bathroom. It would be unfair to say that they do not address the issue, since both the shoes and the belt buckle are mentioned. However, this can work just in a cartoon, since he could wear without any issue and looking absolutely dapper the jacket and shirt of an obese guy. Anyone trying that in reality wouldn't just have to tighten the belt.
Reika Hayami and the Uninvited Guest - S1-E5
Stupidity: A rather unnecessary part of the plot focuses on the convict trying to learn Reika's last name by ordering something on her behalf to read the name on the bill. That's absurd; he couldn't possibly know if the bill would just have the number of the cabin on it instead, or the production company's, and quite frankly for such a VIP (the cruise itself was a one-evening trip around the bay just so fans could spend time with their idol Reika, and he knew that) the ship wouldn't even charge anything for a drink brought to her room.
The Hong Kong Kowloon Treasure Murder Case File 3 - S1-E3
Stupidity: The plan of the murderer involved tying a wire between two different building. To do that, they needed access to the victim's apartment, and to set the trick in advance. The problem is that they tied the wire to a pillar in the middle of the apartment, below eye-level and well in advance; since they spent basically the whole afternoon with Kindaichi (and they met him by chance) the timing of the plan wouldn't work. He'd have literally walked into the trap just coming back home.
