The Ojamanbou Murder Case

Resolution
Hide= Hideyuki Nakayama is the killer...he put the favorite instrument of the victim in the ground and he placed the truck in front of the murder scene so he would see the reflection of the victim using his binoculars and he would know when to let go the metals above that would cause the victim's death. Conan found out because of the camera installed by Nakayama's company in the rooftop. This would later confirm his guilt as he would be caught (in a reflection) by his own surveillance footage. He killed Tsunehisa because he broke up with Hideyuki's sister, causing her to go a spiral of depression and later suicide.
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Because Ran was blocking the mirror to check her hair, Hideyuki dropped the beam too earlier, hence why the victim's fingerprints are not on the harmonica.