Three Hotta Siblings Murder Case

Situation
A lazy drive through the country lands Kogoro, Ran, and Conan in the middle of a murder mystery surrounding the death of billionaire industrialist, Kosaku Hotta. As Conan tries to unravel the clues before the killer can strike again, he faces one disturbing reality: The prime suspects are the victim's children?! It's an explosive whodunit you won't want to miss!

Resolution
Hide= The killer is Masahiro Yamauchi. The man who was Fumiko's lover was his son, Kentarou Yamauchi. He was a deceased piano player. When he and Fumiko got in a relationship and Hotta Sr. objected, they tried to convince him otherwise, but in reply Hotta broke the younger Yamauchi's hand which left him unable to play anymore. The younger Yamauchi fell into despair and killed himself by driving into a nearby cliff. His father then became the family butler only to get revenge, preparing the bomb that killed Hotta Sr.
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The bomb used was the wine container that Ryoji was intending to give to her father. Yamauchi added an unstable components of garden fertilizer, which contained sulfur, and friction matches and a striking pad, so that when the wine container lid was slid open, the matches would rub again the pad and ignite, causing the mixture to explode and to kill Kosaku Hotta. Being a gardener/butler means that Yamauchi is the only individual who could prepare the bomb.

Yamauchi had also planned to kill Fumiko by tampering with her car, mistakenly thinking that she had rejected his son after the incident. In reality, Fumiko was very traumatized as well: she showed it by dressing in black like a widow and wearing a pendant with a photo of her lost love. Fortunately, Yamauchi's trap failed because Conan alerted Fumiko and she returned to the mansion, making Yamauchi break down in tears for misjudging her.

Trivia

 * Ryoji Hotta car drive is a 1978 Red Porsche 928.