The culprit is Shinsuke Akiyama. He faked his own death using Takeda's lifeless body (whom he first strangled, then he decapitated) as a decoy, and was aiming to kill Saegusa and Yamato too. His motive is that years ago, Yamato and his companions's mistakes led to a serial killer terrorizing Nagano before being shot dead, and one of his victims was Akiyama's beloved middle school-aged sister, Aburakawa Tsuyako, who was his only relative. His chosen name Bishamonten was his selfperception as a punisher of evildoers.
Murder (Past)
Location:unknown
Victim:Aburakawa Tsuyako
Cause of death:Gunshot through the forehead
Suspects:unnamed culprit
During the amok run of Yamamoto's drug-addicted friend, the culprit fired several wild shots, and one bullet pierced the forehead of middle schooler Aburakawa Tsuyako, killing her instantly. In turn, the shooter was killed by Takeda.
The Takeda Squad was not accidentally formed by individuals who bore names similar to some of the famous generals of Takeda Shingen. In fact, as Conan, Yamato and Morufushi have found out, the Takeda Squad formed the notorious Woodpecker Society; the "X" imprint left on the victims' bodies pointed to the letter X being the 24th letter of the Western alphabet, corresponding to Takeda Shingen's 24 Generals. In order to complete this inner circle, they were looking for new members; hence they also attempted to recruit Yamamoto, whose name as akin to Takeda's general Yamamoto Kansuke. The reason why Akiyama targeted the Takeda Squad for extermination was that the Squad/Society members seized and sold confiscated guns to criminal elements in order to line their pockets, and it was one of these guns which killed Tsuyako. Akiyama targeted Kansuke because it was his drug-addicted friend who fired the fatal shot.
Season 24 (2019)