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.