Rumi used a cell phone recording trick to manipulate the timeline of the murder. By filming vertically, she was able to hide specific movements while playing a recorded keyboard track to make it seem as though Hagie was still alive and sleeping during the rehearsal.
Amuro (Rei Furuya) inwardly reflects on Scotch’s death, maintaining his bitter belief that Shuichi Akai was the one who killed him—a core conflict that drives much of their rivalry in the series. The Unfriendly Girls Band ~ Part 2 - Detective Conan Wiki Detective Conan Episode 837
The murder was fueled by a tragic misunderstanding regarding a former bandmate, Akane, who had committed suicide. Rumi believed Hagie's harsh words about Akane’s voice drove her to it, though it was later revealed Akane actually died in a selfless accident while trying to save a child. Major Plot Developments Rumi used a cell phone recording trick to
Beyond the immediate case, this episode is a "manga-canon" entry crucial for its character reveals: The Unfriendly Girls Band ~ Part 2 -