- First Murder
- Victim: Hideo Kawashima
- Cause of Death: Drowning
- Location: Piano Room
- Time of Death: 30 minutes – 1 hour before being found
- The first movement of the Moonlight Sonata was played from a tape recorder.
- There was a sea water trail from the door to Kawashima's body and he has dirt and sand on the back of his shirt.
- Kawashima's jacket was found on the beach.
- The doors and windows of the piano room were locked from the inside.
- There were several minutes of silence at the beginning of the tape.
- The Moonlight Sonata sheet music was found, but the notes in the fourth bar were “strange”.
- Conan decoded that the “strange” notes actually say: "The hellfire of hatred made you pay."
- Second Murder
- Victim: Tatsuji Kuroiwa
- Cause of Death: Stabbed to death
- Location: Broadcasting Room
- Time of Death: 5 minutes and 30 seconds before being found
G A G A E E C♯ D F B♭ A E D♯ F D♯ F E A B A A C♯ B♭ B B♭ A B♭ C A
"You realize it don't you? You're next." ("Wakatteru na? Tsugi ha omae no ban da.")
- The second movement of the Moonlight Sonata was played.
- Nishimoto discovered the body.
- The tape has 5 minutes and 30 seconds lead in silence.
- Music notes written with the victim's blood were found.
- Conan decoded the music notes: "You realize it don't you? You're next."
- Third Murder
- Murder: Ken Nishimoto
- Cause of Death: Hanging
- Location: Storage Room
- Time of Death: 30 minutes before being found
- The third movement of the Moonlight Sonata was set to play.
- Sheet music that looked liked a suicide note was found under his feet. The decoded note said he regretted killing Kawashima and Kuroiwa and that he didn't want people to find out the wrongdoing they did years ago.
- There was no chair or anything to stand on, so Nishimoto couldn't hang himself.
- No one would bother writing a suicide note in code.
- Other incriminating evidence:
- The dusty piano in the city hall was tuned perfectly.
- After the first murder, there was someone outside the piano room whom Conan and Kogoro failed to catch.
- When the gang returned to the city hall after the second murder, there was someone in the piano room who jumped out the window and Murasawa was found unconscious on the floor.
- After the third murder, Conan returned to the piano room and found a tuning hammer for the piano.
- Under the piano was a secret drawer with drugs in it.
- Upon looking at the pictures of the crime scene where Kuroiwa was murdered, there was a button with its red light on near the victim's neck.
- Conan found that Hirata has powder-like substance under his sleeves and his left hand was bandaged. He also had lots of foreign money with him.
- Keiji Asou left sheet music in his safe to which it read: “To my son, Seiji”. Asou had a son who became ill when he was a child and had to be hospitalized.
The person who knocked out Murasawa in the piano room was Hirata. The bandage on his left hand was the result of smashing the window when he was trying to escape. He was also the one that Kogoro and Conan chased outside the piano room. The piano room was his meeting place with Kawashima when doing business: dealing drugs. He was using the piano's secret compartment as a hiding place of drugs he got from overseas to which he exchanged later for large sums of money. The reason why he was always talking about the cursed piano was because he wanted to keep everyone in the town away from it. Murasawa saw the drugs that he had left in there earlier so he hit him. Still, he was unrelated to the murders because he wouldn't have related the piano to the crimes.
In the second murder, they found that he had been dead for only a few minutes but when Conan fell on the code of blood, it didn't smear when it takes 25-30 minutes for human blood to dry. It was just a trick that the killer used to manipulate the time of death of the victim. Upon looking at the pictures, there was a button that was lighted near Kuroiwa's neck. But after the body was moved, the light was turned off. This was actually the reverse button. While the police weren't looking, the killer turned off the light. The killer used the reverse side (the blank side that didn't have the song), which played for over 30 min and then it reversed. That was when the 5 minutes and 30 seconds of gap played before the music started.
In the third murder, the killer didn't have the time to put a chair or desk at Nishimoto's feet because he had to escape in time. The killer was probably male because the murders required a lot of physical strength.
The purpose of drowning Kawashima was to send the forensic examiner back to Tokyo, because it was impossible to do an autopsy on the island. The tape in the second murder was a setup so the killer could create an alibi.
Conan deduced that the killer was Narumi Asai and that she was, in fact, Asou's son, Seiji Asou. Asai was probably the surname of the family that adopted him. After graduation, he came to the island as a female doctor. The pronunciation of his name was not written on his diploma, nor the medical license, because if they checked his history, they would have found out that he was a man. He stayed all night so that they'd make him last for questioning.
As for Murasawa, he was an admirer of the late Asou and he was the one who kept the donated piano in tune just like that night.
Seiji then committed suicide by dying like his father. Conan failed to stop him, but he played one last music code message in the burning flames: "Thank you, little detective."
Seiji's motive dated back when his father, the pianist, and his family was murdered. Kawashima, Nishimoto, Kuroiwa, and Kameyama used Asou's international concerts as a front for their international drug trade. When Asou stated that he wouldn't cooperate any longer, they got scared that their secret might be exposed. This was all written in the sheet music that he left behind in the safe as his confession to his son. Seiji was hospitalized in Tokyo at the time of the murder.
Seiji went back to the island to avenge his family's death. When he told Kameyama that he was Asou's son, the late mayor was terrified and told him everything. He then had a heart attack. Seiji played the Moonlight Sonata that his father loved so much upon seeing the mayor dead.
